crash: supplied history does not follow left-hand parents

Variation on the screwed up history bug:
(rpg+helper) >bzr branch lp:rpg+helper edit_char_name
bzr: ERROR: bzrlib.errors.NotLefthandHistory: Supplied history does not follow left-hand parents

I remember what I've done to my repo to get here.

1. Create repo on website.
2. Associate with main dev on project.
3. bzr checkout lp:rpg+helper \bzrrepo\main (which was set up with --no-trees)
4. bzr checkout \bzrrepo\main virtualenv\rpghelper\main
5. bzr branch virtualenv\rpghelper\main virtualenv\rpghelper\tg2_setup
6. commit several times to tg2_setup
7. cd virtualenv\rpghelper\main; bzr merge ..\tg2_setup
8. bzr update
9. bzr qcommit
-- Things start looking very funny here --
10. Commit fails, b/c checkout of a checkout is apparently not OK.
11. rmdir /s /q virtualenv\rpghelper\main
12. bzr checkout lp:rpg+helper virtualenv\rpghelper\main
13. cd virtualenv\rpghelper\main
14. bzr up
15. bzr merge ..\tg2_setup
16. bzr qcommit
-- Everything is all screwed up now. qlog shows a history on both lp:rpg+helper & virtualenv\rpghelper\main that does not show anything about the tg2_setup branch - i tlooks like jus tmainline development. My working tree of main has no files in it. local rmdir & bzr up get me files, but qlog is still funny. --
17. bzr branch lp:rpg+helper
-- The error happens. --

I've got a fairly short history, but managed to do several things wrong during it (I'm still new to bzr). I hope this helps you figure out what series of bzr commands is able to corrupt the history of a branch.

I don't know how I should go about cleaning the history on this project. I could blow away the main branch & start over - I've got the current files - but I really don't like doing that, even if I'd just lose a 4-commit history. At least, I don't want that to be the solution until I've also done something to prevent this from happening again.