Format "unnamed" when creating "default" branches in newer repository formats

I'm using bzr 1.9rc1 with Python 2.6, on Windows XP.

Here's what happens when a default repository and a branch is created. Repository and branch are in pack-0.92 format.
C:\tmp$ mkdir repo && cd repo

C:\tmp\repo$ bzr init-repo .
Shared repository with trees (format: pack-0.92)
Location:
  shared repository: .

C:\tmp\repo$ bzr init trunk
Repository tree (format: pack-0.92)
Location:
  shared repository: .
  repository branch: trunk

Here's the output for a rich-root-pack repository. Note that the branch is also rich-root-pack.
C:\tmp$ mkdir repo && cd repo

C:\tmp\repo$ bzr init-repo --rich-root-pack .
Shared repository with trees (format: rich-root-pack)
Location:
  shared repository: .

C:\tmp\repo$ bzr init trunk
Repository tree (format: rich-root-pack)
Location:
  shared repository: .
  repository branch: trunk

Here's a 1.6 repository. Note that the branch is in format "unnamed."
C:\tmp\repo$ bzr init-repo --1.6 .
Shared repository with trees (format: 1.6)
Location:
  shared repository: .

C:\tmp\repo$ bzr init trunk
Repository tree (format: unnamed)
Location:
  shared repository: .
  repository branch: trunk

I would have expected format "1.6." The content of .bzr/branch/format is:
    Bazaar Branch Format 6 (bzr 0.15)

When creating a branch with "bzr init --1.6 trunk" the format is:
    Bazaar Branch Format 7 (needs bzr 1.6)