Comment 2 for bug 402022

I don't understand how this can be causing a test failure and not pqm failures. Perhaps it's actually caused by a plugin, though not one visible in the traceback.

Indeed the problem is caused by qbzr hooking in here:

(Pdb) p self._do_preview
<bound method cmd_merge._do_preview of <bzrlib.plugins.qbzr.lib.commands.cmd_merge object at 0x18204d0>>