Here is a complete use-case (maybe not relevant but reproducing my problem) :

Initialization :

/tmp $ bzr init-repo repo
Shared repository with trees (format: 2a)
Location:
  shared repository: repo
/tmp $ cd repo
/tmp/repo $ mkdir datas
/tmp/repo $ bzr init datas/dev_datas
Created a repository tree (format: 2a)                                                                                                                                                                                                                                             
Using shared repository: /home/alex/tmp/repo/
/tmp/repo $ mkdir work
/tmp/repo $ cd work/
/tmp/repo/work $ bzr init branch
Created a repository tree (format: 2a)
Using shared repository: /home/alex/tmp/repo/
/tmp/repo/work $ bzr co branch/ checkout

Launching bzr explorer :
$ bzr explorer
Ctrl+o --> /tmp/repo/work/

Result : it opens the whole repository /tmp/repo and not just the folder /tmp/repo/work/ (cf. attachment)

Logs when printing 'path' at line 163 of bzrlib/transport/local.py :
/home/alex/.bzr/branch-format
/home/.bzr/branch-format
/.bzr/branch-format
/tmp/repo/work/.bzr/branch-format
/tmp/repo/.bzr/branch-format
/tmp/repo/.bzr/checkout/format
/tmp/repo/.bzr/branch/format
/tmp/repo/.bzr/repository/format
/tmp/repo/.bzr/branch-format
/tmp/repo/.bzr/.bzr/branch-format
/tmp/repo/.bzr/README/.bzr/branch-format
/tmp/repo/.bzr/branch-format/.bzr/branch-format
/tmp/repo/.bzr/branch-lock/.bzr/branch-format
/tmp/repo/.bzr/repository/.bzr/branch-format
/tmp/repo/.bzr/repository/format/.bzr/branch-format
/tmp/repo/.bzr/repository/indices/.bzr/branch-format
/tmp/repo/.bzr/repository/lock/.bzr/branch-format
/tmp/repo/.bzr/repository/obsolete_packs/.bzr/branch-format
/tmp/repo/.bzr/repository/pack-names/.bzr/branch-format
/tmp/repo/.bzr/repository/packs/.bzr/branch-format
/tmp/repo/.bzr/repository/shared-storage/.bzr/branch-format
/tmp/repo/.bzr/repository/upload/.bzr/branch-format
/tmp/repo/datas/.bzr/branch-format
/tmp/repo/datas/dev_datas/.bzr/branch-format
/tmp/repo/datas/dev_datas/.bzr/branch/format
/tmp/repo/datas/dev_datas/.bzr/repository/format
/tmp/repo/datas/.bzr/branch-format
/tmp/repo/.bzr/branch-format
/tmp/repo/.bzr/repository/format
/tmp/repo/datas/dev_datas/.bzr/branch/branch.conf
/tmp/repo/datas/dev_datas/.bzr/branch/format
/tmp/repo/datas/dev_datas/.bzr/branch/branch.conf
/tmp/repo/.bzr/repository/pack-names
/tmp/repo/datas/dev_datas/.bzr/branch/branch.conf
/tmp/repo/work/.bzr/branch-format
/tmp/repo/work/branch/.bzr/branch-format
/tmp/repo/work/branch/.bzr/branch/format
/tmp/repo/work/branch/.bzr/repository/format
/tmp/repo/work/.bzr/branch-format
/tmp/repo/.bzr/branch-format
/tmp/repo/.bzr/repository/format
/tmp/repo/work/branch/.bzr/branch/branch.conf
/tmp/repo/work/branch/.bzr/branch/format
/tmp/repo/work/branch/.bzr/branch/branch.conf
/tmp/repo/.bzr/repository/pack-names
/tmp/repo/work/branch/.bzr/branch/branch.conf
/tmp/repo/work/checkout/.bzr/branch-format
/tmp/repo/work/checkout/.bzr/branch/format
/tmp/repo/work/checkout/.bzr/repository/format
/tmp/repo/work/.bzr/branch-format
/tmp/repo/.bzr/branch-format
/tmp/repo/.bzr/repository/format
/tmp/repo/work/checkout/.bzr/branch/branch.conf
/tmp/repo/work/checkout/.bzr/branch/format
/tmp/repo/work/checkout/.bzr/branch/branch.conf
/tmp/repo/work/checkout/.bzr/branch/branch.conf