I have read T4333 but still don't now why it doesn't work for me.
Situation: A differential D12345 was created by another user, was accepted and is ready to land. He/she doesn't have access rights so i tried landing it:

• arc patch D12345: The branch with the commit is created. Author is me and date is current (which is already wrong?)
• arc land--hold : correct detection

This branch has revision 'D12345: bla..." but you are not the author. Land this revision by xyz?

->y
Nothing changes, I'm still author.

With --trace I can see

[39] <exec> $ git commit --author 'Alex...

Ok, author is still me, but why?

Reproducible: always

arc version:

arcanist 224986af634e1dfc40916e5baee76897db4c907f (8 Feb 2017)
libphutil 82f71f62129bc19f28aeed8c660c931e512a66e7 (9 Feb 2017)

I cannot determine the version for phabricator.kde.org because I'm not admin (and I ask myself why version information is restricted)