--username wrong or ignored for git-svn

Hello,

Just now I attempted to commit some changes that a coworker had made to our subversion repository using git-svn. Since it was his work, we attempted to commit it using his username, though it was done in a git repository that I'd previously used with my username. So I did:

git-svn dcommit --username <name>

But it ignored --username and the commit is now attributed to me. Is it because I'd previously done dcommit in my own username? There was no warning that it wouldn't do what I expected.

Admittedly it's was a weird thing to have him make a change in my local repository but we didn't think it would be a problem if we carefully used --username.

thanks, Steve