I don't know if it is a bug or more a feature request:

• Currently you can add tasks to a revision by typing "maniphest tasks: T123" in arcanist for example.
• If a task was added to a differential revision it is useful to add the task to the commit too.
• Add the momentan you have to write "ref T123" or something else, this in my opinion not useful, because arcanist writes still "maniphest tasks: T123" at the commit summary, so this information is a duplicate
• In my opinion it is more useful to automaticaly add this task to the commit, if this was not wanted, the user can remove the task, or can add it manualy to the differential revision