Sure, creating a circular dependency isn't cool. But when someone //does// make that mistake, it currently "hangs" the UI, leaving the grey shading in place until the page is refreshed. Behind the scenes, the logs show:
```
PHP message: [2015-03-03 09:43:46] EXCEPTION: (PhabricatorEdgeCycleException) Graph cycle detected (type=3, cycle=PHID-TASK-ve2obkgjfvjevd5qvtnr, PHID-TASK-qfcevk7tkhm5hfvk5dst, PHID-TASK-ve2obkgjfvjevd5qvtnr). at [<phabricator>/src/infrastructure/edges/editor/PhabricatorEdgeEditor.php:401]
PHP message: arcanist(head=master, ref.master=d8182cf55d50), phabricator(head=master, ref.master=18340d9ceffe), phutil(head=master, ref.master=b6200342f224)
PHP message: #0 PhabricatorEdgeEditor::detectCycles(array, integer) called at [<phabricator>/src/infrastructure/edges/editor/PhabricatorEdgeEditor.php:129]
PHP message: #1 PhabricatorEdgeEditor::save() called at [<phabricator>/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php:481]
PHP message: #2 PhabricatorApplicationTransactionEditor::applyExternalEffects(ManiphestTask, ManiphestTransaction) called at [<phabricator>/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php:717]
PHP message: #3 PhabricatorApplicationTransactionEditor::applyTransactions(ManiphestTask, array) called at [<phabricator>/src/applications/search/controller/PhabricatorSearchAttachController.php:89]
PHP message: #4 PhabricatorSearchAttachController::processRequest() called at [<phabricator>/src/aphront/AphrontController.php:33]
PHP message: #5 AphrontController::handleRequest(AphrontRequest) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:196]
PHP message: #6 AphrontApplicationConfiguration::processRequest(AphrontRequest, PhutilDeferredLog, AphrontPHPHTTPSink) called at [<phabricator>/src/aphront/configuration/AphrontApplicationConfiguration.php:121]
PHP message: #7 AphrontApplicationConfiguration::runHTTPRequest(AphrontPHPHTTPSink) called at [<phabricator>/webroot/index.php:19]
```
I'd expect, instead, that some sort of "you screwed up" message would appear, informing the user of their mistake.