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.