Dear Ben,
apparently the problem you are experiencing is the same as the one reported by Rene Zamseil http://alice.wu-wien.ac.at:8000/xotcl-mailing-list/1060.html
This bug is fixed in the current development verison of XOTcl, which you can get via git with
git clone git://alice.wu-wien.ac.at/xotcl
Version 1.6.1 should be released in the near future.
best regards -gustaf neumann