I think this bug has been fixed in bzr 1.18rc1 by John, but Launchpad is still running 1.17. Specifically John fixed some bugs where CHK repositories would generate XML inventories (and non-rich-root ones at that!) via some code paths. He fixed this as part of fixing bzr send of 2a repositories (bug 393349), I think.
So I think this will probably be fixed when Launchpad next upgrades their version of bzr.
I think this bug has been fixed in bzr 1.18rc1 by John, but Launchpad is still running 1.17. Specifically John fixed some bugs where CHK repositories would generate XML inventories (and non-rich-root ones at that!) via some code paths. He fixed this as part of fixing bzr send of 2a repositories (bug 393349), I think.
So I think this will probably be fixed when Launchpad next upgrades their version of bzr.