A possibly related issue is that "bzr merge --force -r A..B" will add the A..B to the pending merges (i.e. will keep track of history) if A is already present in the branch, but not if A is only present in the pending merges.
A possibly related issue is that "bzr merge --force -r A..B" will add the A..B to the pending merges (i.e. will keep track of history) if A is already present in the branch, but not if A is only present in the pending merges.