https://secure.phabricator.com/transactions/editengine/paste.paste/view/7/ phlogs an exception:
implode(): Invalid arguments passed Stack trace: implode called at [/core/lib/phabricator/src/applications/transactions/editfield/PhabricatorTextAreaEditField.php:54] PhabricatorTextAreaEditField::getValueForControl called at [/core/lib/phabricator/src/applications/transactions/editfield/PhabricatorEditField.php:290] PhabricatorEditField::buildControl called at [/core/lib/phabricator/src/applications/transactions/editfield/PhabricatorEditField.php:317] PhabricatorEditField::renderControl called at [/core/lib/phabricator/src/applications/transactions/editfield/PhabricatorEditField.php:347] PhabricatorEditField::appendToForm called at [/core/lib/phabricator/src/applications/transactions/controller/PhabricatorEditEngineConfigurationViewController.php:234] PhabricatorEditEngineConfigurationViewController::buildFieldList called at [/core/lib/phabricator/src/applications/transactions/controller/PhabricatorEditEngineConfigurationViewController.php:40] PhabricatorEditEngineConfigurationViewController::handleRequest called at [/core/lib/phabricator/src/aphront/configuration/AphrontApplicationConfiguration.php:237] AphrontApplicationConfiguration::processRequest called at [/core/lib/phabricator/src/aphront/configuration/AphrontApplicationConfiguration.php:149] AphrontApplicationConfiguration::runHTTPRequest called at [/core/lib/phabricator/webroot/index.php:17]
Only does that for Paste forms, so probably a typo somewhere in Project config.
(I've noticed it locally while navigating to edit some unrelated form)