I don't really know if Maniphest is the right project but it may be the one which is affected by the lack of "offline optimistic locking" mechanisms.

Take notice of the following case:

1. User A creates the task
2. User B (who has edit privileges to a maniphest task) opens the task for editing and adds a project, renames a task, adds users to cc, whatever and saves.
3. User C (who has edit privileges to a maniphest task), unaware of the changes which are pending by User B, grabs the version of the original task created by user A for editing and creates his own changes and when saving, he overwrites that user B has done.

It would be good to have User C notified that he's editing an out-of-date version of the Task when he tries to save it.