I am not having any luck throwing away historical data using `git annex forget`. According to the manpage "the forgetfulness will automatically propagate out", but what I observe is that the old metadata is merged right back into the branch with the truncated metadata:

```
$ git annex forget --force --drop-dead
$ git annex sync B3
$ git log --branches --remotes --oneline --graph
*   e7cf462ada (B3/synced/git-annex, B3/git-annex, git-annex) merging B3/git-annex into git-annex
|\  
| * 7f8b737a01 update
* | 41bef1e3db merging B3/git-annex into git-annex
|\| 
| * 383a53bf9a update
| *   2607574ed0 merging B3/git-annex into git-annex
| |\  
| | * dc46f334c9 update
| * | c4c25c52a7 new branch for transition ["forget git history","forget dead remotes"]
|  /  
* / d3a1042f9e new branch for transition ["forget git history","forget dead remotes"]
 /
 |
(here comes all of the old history)
```

What else do I have to do to make this happen?

Thanks for your support! -- Jonas
