Hello Joachim,
bzr merge is different than eg. git merge.
This is actually one of the reasons why we have switched to bazaar: you are in complete control!
This means, bzr will never commit things without you initiating it.
When you do a merge, you have to commit the merge in a second step to your branch.
This is also the reason why Bazaar does not allow merging if you still have uncommitted changes in your branch.
I hope this makes sense.
Timotheus