While testing a moin 2.0 bug fix, whoosh 2.4.0 caused a traceback pointing to line 117 in codec/legacy.py. This happened while trying to save a new moin-wiki page. The traceback was not saved and now the problem cannot be reproduced.
A guess is:
offset = self.dataoffset + self.idslen + self.weightslen
offset = self.dataoffset + self.idslen + self.wtslen
Sorry for not saving the traceback.