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It would be good to have User C notified that he's editing an out-of-date version of the Task when he tries to save it.