bzr-1.7rc1 bzr branch --stacked problem/question

[David Ingamells]

The following command works with bzr-1.6.1 where bzr info gives the 
following about the repos:

Repository branch (format: pack-0.92)
Location:
  shared repository: /home/CmsRoot/repos/CVTOOL
  repository branch: .



bzr branch --verbose --stacked bzr+ssh://mscvs01/<path> <to>



However with bzr-1.7rc1 the following error arises:


Source format does not support stacking, using format: '1.6'
  Packs 5 (adds stacking support, requires bzr 1.6)

bzr: ERROR: The branch 'file://<to>'(Bazaar Branch Format 6 (bzr 0.15)) 
is not a stackable format. You will need to upgrade the branch to permit 
branch stacking.
bzrbranch returned status 3
FATAL: command branch failed with status 3
 

since bzr is MAKING the named branch why does it then complain that the 
format is no good?

Do I need to upgrade the repos to use --stacked now?