I have no idea how it happened (I didn't do it on purpose), but I was able to vote for my own edit:
Agreed to fix within 12 months by http://scheduling.ocharles.org.uk and http://chatlogs.musicbrainz.org/musicbrainz-devel/2012/2012-03/2012-03-26.html#T19-36-54-3898
This seems to be pretty easy to do intentionally (or programatically). There is no validation that the voting user is not the same as the editor.
Login, saving session cookies:
wget --keep-session-cookies --save-cookies cookies.txt --post-data 'username=Hawke&password=xxxxx' http://musicbrainz.org/login
wget --load-cookies cookies.txt --post-data 'url=http://musicbrainz.org/edit/16944694&enter-vote.vote.0.edit_id=16944694&enter-vote.vote.0.vote=1&submit=Enter vote' http://musicbrainz.org/edit/enter_votes
This is in review at http://codereview.musicbrainz.org/r/1961/ and available for testing at http://test.musicbrainz.org/
The origin/mbs-3904 branch is now in beta testing.