Weird git-svn story - how can I fix this?

I am relatively new to git, using Subversion primarily in the past. I recently cloned a Subversion repository with my changes and then set up a remote open git repository that the developer developers will use when we move to git. I haven't made any changes to the SVN repository yet (at least I didn't do it on purpose!). I tried to push new changes from Subversion with git svn rebase, and that's where the problem started. I think the best illustration of my problem comes from gitk:

Any ideas on how to remove this duplicate history?

This looks like it helped (from helpful people at #git):

git rebase --onto master~2^1 master~2 master

      

        
        
        
      

    

What does it do?