diff --git a/src/applications/maniphest/__tests__/ManiphestTaskTestCase.php b/src/applications/maniphest/__tests__/ManiphestTaskTestCase.php
--- a/src/applications/maniphest/__tests__/ManiphestTaskTestCase.php
+++ b/src/applications/maniphest/__tests__/ManiphestTaskTestCase.php
@@ -15,9 +15,11 @@
     $t2 = $this->newTask($viewer, 'Task 2');
     $t3 = $this->newTask($viewer, 'Task 3');
 
+    $auto_base = min(mpull(array($t1, $t2, $t3), 'getID'));
+
 
     // Default order should be reverse creation.
-    $tasks = $this->loadTasks($viewer);
+    $tasks = $this->loadTasks($viewer, $auto_base);
     $t1 = $tasks[1];
     $t2 = $tasks[2];
     $t3 = $tasks[3];
@@ -26,7 +28,7 @@
 
     // Move T3 to the middle.
     $this->moveTask($viewer, $t3, $t2, true);
-    $tasks = $this->loadTasks($viewer);
+    $tasks = $this->loadTasks($viewer, $auto_base);
     $t1 = $tasks[1];
     $t2 = $tasks[2];
     $t3 = $tasks[3];
@@ -35,7 +37,7 @@
 
     // Move T3 to the end.
     $this->moveTask($viewer, $t3, $t1, true);
-    $tasks = $this->loadTasks($viewer);
+    $tasks = $this->loadTasks($viewer, $auto_base);
     $t1 = $tasks[1];
     $t2 = $tasks[2];
     $t3 = $tasks[3];
@@ -44,7 +46,7 @@
 
     // Repeat the move above, there should be no overall change in order.
     $this->moveTask($viewer, $t3, $t1, true);
-    $tasks = $this->loadTasks($viewer);
+    $tasks = $this->loadTasks($viewer, $auto_base);
     $t1 = $tasks[1];
     $t2 = $tasks[2];
     $t3 = $tasks[3];
@@ -53,7 +55,7 @@
 
     // Move T3 to the first slot in the priority.
     $this->movePriority($viewer, $t3, $t3->getPriority(), false);
-    $tasks = $this->loadTasks($viewer);
+    $tasks = $this->loadTasks($viewer, $auto_base);
     $t1 = $tasks[1];
     $t2 = $tasks[2];
     $t3 = $tasks[3];
@@ -62,7 +64,7 @@
 
     // Move T3 to the last slot in the priority.
     $this->movePriority($viewer, $t3, $t3->getPriority(), true);
-    $tasks = $this->loadTasks($viewer);
+    $tasks = $this->loadTasks($viewer, $auto_base);
     $t1 = $tasks[1];
     $t2 = $tasks[2];
     $t3 = $tasks[3];
@@ -71,7 +73,7 @@
 
     // Move T3 before T2.
     $this->moveTask($viewer, $t3, $t2, false);
-    $tasks = $this->loadTasks($viewer);
+    $tasks = $this->loadTasks($viewer, $auto_base);
     $t1 = $tasks[1];
     $t2 = $tasks[2];
     $t3 = $tasks[3];
@@ -80,7 +82,7 @@
 
     // Move T3 before T1.
     $this->moveTask($viewer, $t3, $t1, false);
-    $tasks = $this->loadTasks($viewer);
+    $tasks = $this->loadTasks($viewer, $auto_base);
     $t1 = $tasks[1];
     $t2 = $tasks[2];
     $t3 = $tasks[3];
@@ -88,6 +90,43 @@
 
   }
 
+  public function testTaskAdjacentBlocks() {
+    $viewer = $this->generateNewTestUser();
+
+    $t = array();
+    for ($ii = 1; $ii < 10; $ii++) {
+      $t[$ii] = $this->newTask($viewer, "Task Block {$ii}");
+
+      // This makes sure this test remains meaningful if we begin assigning
+      // subpriorities when tasks are created.
+      $t[$ii]->setSubpriority(0)->save();
+    }
+
+    $auto_base = min(mpull($t, 'getID'));
+
+    $tasks = $this->loadTasks($viewer, $auto_base);
+    $this->assertEqual(
+      array(9, 8, 7, 6, 5, 4, 3, 2, 1),
+      array_keys($tasks));
+
+    $this->moveTask($viewer, $t[9], $t[8], true);
+    $tasks = $this->loadTasks($viewer, $auto_base);
+    $this->assertEqual(
+      array(8, 9, 7, 6, 5, 4, 3, 2, 1),
+      array_keys($tasks));
+
+    // When there is a large block of tasks which all have the same
+    // subpriority, they should be assigned distinct subpriorities as a
+    // side effect of having a task moved into the block.
+
+    $subpri = mpull($tasks, 'getSubpriority');
+    $unique_subpri = array_unique($subpri);
+    $this->assertEqual(
+      9,
+      count($subpri),
+      'Expected subpriorities to be distributed.');
+  }
+
   private function newTask(PhabricatorUser $viewer, $title) {
     $task = ManiphestTask::initializeNewTask($viewer);
 
@@ -103,15 +142,23 @@
     return $task;
   }
 
-  private function loadTasks(PhabricatorUser $viewer) {
+  private function loadTasks(PhabricatorUser $viewer, $auto_base) {
     $tasks = id(new ManiphestTaskQuery())
       ->setViewer($viewer)
       ->setOrderBy(ManiphestTaskQuery::ORDER_PRIORITY)
       ->execute();
 
-    $tasks = mpull($tasks, null, 'getID');
+    // NOTE: AUTO_INCREMENT changes survive ROLLBACK, and we can't throw them
+    // away without committing the current transaction, so we adjust the
+    // apparent task IDs as though the first one had been ID 1. This makes the
+    // tests a little easier to understand.
+
+    $map = array();
+    foreach ($tasks as $task) {
+      $map[($task->getID() - $auto_base) + 1] = $task;
+    }
 
-    return $tasks;
+    return $map;
   }
 
   private function moveTask(PhabricatorUser $viewer, $src, $dst, $is_after) {
diff --git a/src/applications/maniphest/editor/ManiphestTransactionEditor.php b/src/applications/maniphest/editor/ManiphestTransactionEditor.php
--- a/src/applications/maniphest/editor/ManiphestTransactionEditor.php
+++ b/src/applications/maniphest/editor/ManiphestTransactionEditor.php
@@ -679,21 +679,57 @@
     // return the result.
     if ($adjacent) {
       // If the adjacent task has a subpriority that is identical or very
-      // close to the task we're looking at, we're going to move it a little
-      // farther down the subpriority list.
+      // close to the task we're looking at, we're going to move it and all
+      // tasks with the same subpriority a little farther down the subpriority
+      // scale.
       if (abs($adjacent->getSubpriority() - $base) < 0.01) {
+        $conn_w = $adjacent->establishConnection('w');
+
+        // Get all of the tasks with the same subpriority as the adjacent
+        // task, including the adjacent task itself.
+        $shift_base = $adjacent->getSubpriority();
+        $shift_all = id(new ManiphestTaskQuery())
+          ->setViewer(PhabricatorUser::getOmnipotentUser())
+          ->setOrderBy(ManiphestTaskQuery::ORDER_PRIORITY)
+          ->withPriorities(array($adjacent->getPriority()))
+          ->withSubpriorities(array($shift_base))
+          ->setReversePaging(!$is_after)
+          ->execute();
+        $shift_last = last($shift_all);
+
+        // Find the subpriority before or after the task at the end of the
+        // block.
         list($shift_pri, $shift_sub) = self::getAdjacentSubpriority(
-          $adjacent,
+          $shift_last,
           $is_after);
 
-        queryfx(
-          $adjacent->establishConnection('r'),
-          'UPDATE %T SET subpriority = %f WHERE id = %d',
-          $adjacent->getTableName(),
-          $shift_sub,
-          $adjacent->getID());
+        $delta = ($shift_sub - $shift_base);
+        $count = count($shift_all);
+
+        $shift = array();
+        $cursor = 1;
+        foreach ($shift_all as $shift_task) {
+          $shift_target = $shift_base + (($cursor / $count) * $delta);
+          $cursor++;
+
+          queryfx(
+            $conn_w,
+            'UPDATE %T SET subpriority = %f WHERE id = %d',
+            $adjacent->getTableName(),
+            $shift_target,
+            $shift_task->getID());
+
+          // If we're shifting the adjacent task, update it.
+          if ($shift_task->getID() == $adjacent->getID()) {
+            $adjacent->setSubpriority($shift_target);
+          }
 
-        $adjacent->setSubpriority($shift_sub);
+          // If we're shifting the original target task, update the base
+          // subpriority.
+          if ($shift_task->getID() == $dst->getID()) {
+            $base = $shift_target;
+          }
+        }
       }
 
       $sub = ($adjacent->getSubpriority() + $base) / 2;
diff --git a/src/applications/maniphest/query/ManiphestTaskQuery.php b/src/applications/maniphest/query/ManiphestTaskQuery.php
--- a/src/applications/maniphest/query/ManiphestTaskQuery.php
+++ b/src/applications/maniphest/query/ManiphestTaskQuery.php
@@ -37,6 +37,7 @@
 
   private $statuses;
   private $priorities;
+  private $subpriorities;
 
   private $groupBy          = 'group-none';
   const GROUP_NONE          = 'group-none';
@@ -137,6 +138,11 @@
     return $this;
   }
 
+  public function withSubpriorities(array $subpriorities) {
+    $this->subpriorities = $subpriorities;
+    return $this;
+  }
+
   public function withSubscribers(array $subscribers) {
     $this->subscriberPHIDs = $subscribers;
     return $this;
@@ -506,6 +512,13 @@
         $this->priorities);
     }
 
+    if ($this->subpriorities) {
+      return qsprintf(
+        $conn,
+        'task.subpriority IN (%Lf)',
+        $this->subpriorities);
+    }
+
     return null;
   }
 
diff --git a/src/infrastructure/testing/fixture/PhabricatorStorageFixtureScopeGuard.php b/src/infrastructure/testing/fixture/PhabricatorStorageFixtureScopeGuard.php
--- a/src/infrastructure/testing/fixture/PhabricatorStorageFixtureScopeGuard.php
+++ b/src/infrastructure/testing/fixture/PhabricatorStorageFixtureScopeGuard.php
@@ -11,7 +11,7 @@
     $this->name = $name;
 
     execx(
-      'php %s upgrade --force --namespace %s',
+      'php %s upgrade --force --no-adjust --namespace %s',
       $this->getStorageBinPath(),
       $this->name);