This is a pretty obscure error, but I'm curious what might be causing it!

I made a commit and sent it off for review. The commit message said something like, "In Dxxxx, Fred did some work. Now I do some more work." No problem, the review went off and the git commit message was amended to say: "Differential Revision: http://phabricator.khanacademy.org/Dyyyy."

Then i made another commit on top of that, and ran arc diff --amend. This failed with this error:

Usage Exception: You don't own revision Dxxxx 'Make notification config side-effect-less on load'. You can only update revisions you own.

When I then ran arc diff instead -- without the --amend it properly updated Dyyyy.

I dont' know why adding --amend would change the arc which output, but apparently it did.