git is stating a branch is not merged after rebasing - why?

I'm using git-svn to manage my bugfix branches, but it tells me that I have unmerged changes, even though if I review the SVN repo directly, I can see they have been committed too. It's like the rebase of the bug fix is not setting the branch as merged.

What am I doing wrong, here?

git checkout -b fix_bug_1234

git add .
git commit -m "first change"
git add .
git commit -m "second change"

git rebase -i HEAD~2 // squash the two changes together

git svn rebase // fetch any changes from svn

git checkout master
git rebase fix_bug_1234
git svn dcommit

git branch -d fix_bug_1234
error: The branch 'fix_bug_1234' is not fully merged.