attempting to import a directory/archive containing a .bzr directory gives a fatal "tree transform is malformed" error

I was trying to quickly and naïvely make a branch with the contents of another developer's work but the ancestry of a somewhat "blessed" branch at the moment. I'm happy to work that out a better way, but my quick noodling in /tmp seems to have tickled a bug:

 /tmp$ sudo bzr get /special/place/branch
 Branched 258 revision(s).
 /tmp$ cd branch/
 /tmp/branch$ sudo bzr import /home/developer/hisbranch/
 bzr: ERROR: Tree transform is malformed [('overwrite', 'new-1089', u'lock'), ('overwrite', 'new-1083', u'lock'), ('overwrite', 'new-477', u'branch-format'), ('overwrite', 'new-476', u'branch-lock'), ('overwrite', 'new-475', u'.bzr'), ('overwrite', 'new-1082', u'branch'), ('overwrite', 'new-1081', u'README'), ('overwrite', 'new-1086', u'format'), ('overwrite', 'new-1076', u'format'), ('overwrite', 'new-479', u'lock'), ('overwrite', 'new-478', u'repository'), ('overwrite', 'new-1093', u'conflicts'), ('overwrite', 'new-1091', u'format'), ('overwrite', 'new-1090', u'dirstate'), ('overwrite', 'new-1088', u'checkout')]

And the lock is left held after.

This is repeatable with these two branches.

 Version is: Bazaar (bzr) 1.5

 "Special" branch is: Standalone tree (format: pack-0.92)
 so is the /tmp/branch/.
 Developer branch is: Standalone tree (format: dirstate)