Bulk Change operations are very slow with large number of assignable users

The permissions scheme on our deployment of JIRA was recently changed to enable all users to be assignable. Since that change, bulk operations have become unusable due to slowness. It appears that the assignable user list that appears in Edit operations for instance is loop constructed leading to a multiplicative delay based on the number of issues selected for bulk operations. Please see https://bugreports.qt-project.org/browse/QTJIRA-174 for details.