Currently, we populate a set with git rev-parse --not --branches, delete the new branch from the set, add the current branch into the set, and gather the commits with git rev-list #{set}, essentially.

If you do something like
git checkout master
git branch foo; git push origin foo

You'll get notified for all commits on master that aren't on other branches, since foo and master share the same hash (which gets removed from the set).

Easy fix for this is to use an Array instead of a Set. There are some other corner cases if we push more than one branch at a time, but I'll save that for another ticket.