"Tree transform is malformed" error with "bzr import-dsc"

I'm experimenting with bzr-builddeb and it seems to trigger an error in bzr.

I've tried bzr 0.91-2 from Debian unstable, but it looks the same.

Note: you need bzr-builddeb for reproducing this.

$ bzr import-dsc --to test --snapshot bzr-builddeb
snapshot.debian.net has lost packages from before 12/03/2005, only packages from after that date will be imported.
imported bzr-builddeb_0.11.tar.gz
imported bzr-builddeb_0.14.tar.gz
imported bzr-builddeb_0.15~rc1.tar.gz
imported bzr-builddeb_0.16.tar.gz
imported bzr-builddeb_0.16.1.tar.gz
imported bzr-builddeb_0.16.2.tar.gz
imported bzr-builddeb_0.18.tar.gz
bzr: ERROR: Tree transform is malformed [('overwrite', 'new-299', u'lock'), ('overwrite', 'new-230', u'99'), ('overwrite', 'new-297', u'branch'), ('overwrite', 'new-296', u'conflicts'), ('overwrite', 'new-295', u'merge-hashes'), ('overwrite', 'new-294', u'lock'), ('overwrite', 'new-293', u'dirstate'), ('overwrite', 'new-292', u'format'), ('overwrite', 'new-291', u'checkout'), ('overwrite', 'new-289', u'README'), ('overwrite', 'new-95', u'22'), ('overwrite', 'new-238', u'4a'), ('overwrite', 'new-288', u'revision-store'), ('overwrite', 'new-114', u'3e'), ('overwrite', 'new-283', u'9f'), ('overwrite', 'new-78', u'revisions.kndx'), ('overwrite', 'new-79', u'inventory.knit'), ('overwrite', 'new-74', u'revisions.knit'), ('overwrite', 'new-75', u'format'), ('overwrite', 'new-76', u'lock'), ('overwrite', 'new-77', u'signatures.knit'), ('overwrite', 'new-70', u'branch-lock'), ('overwrite', 'new-71', u'repository'), ('overwrite', 'new-72', u'signatures.kndx'), ('overwrite', 'new-73', u'inventory.kndx'), ('overwrite', 'new-137', u'5a'), ('overwrite', 'new-298', u'format'), ('overwrite', 'new-247', u'32'), ('overwrite', 'new-221', u'98'), ('overwrite', 'new-69', u'.bzr'), ('overwrite', 'new-290', u'branch-format'), ('overwrite', 'new-301', u'branch-name'), ('overwrite', 'new-90', u'7e'), ('overwrite', 'new-84', u'52'), ('overwrite', 'new-80', u'knits'), ('overwrite', 'new-264', u'fc')]
/usr/lib/python2.5/site-packages/bzrlib/lockable_files.py:110: UserWarning: file group LockableFiles(<bzrlib.transport.local.LocalTransport url=file:///tmp/foo/test/.bzr/checkout/>) was not explicitly unlocked
  warn("file group %r was not explicitly unlocked" % self)
/usr/lib/python2.5/site-packages/bzrlib/lock.py:79: UserWarning: lock on <open file u'/tmp/foo/test/.bzr/checkout/dirstate', mode 'rb+' at 0x849db18> not released
  warn("lock on %r not released" % self.f)

It seems to be the bzr-builddeb package itself, which archived content triggers the error: "bzr import-dsc --to test --snapshot hello" works fine.