[Zope] Bug with External Methods and default params?

[Stefan Franke]

(First a little excuse: I've got an extreme lack of time right now,
otherwise I would
try to isolate the problem -- but maybe it's a bug already known)

There seems to be a problem calling external methods with default
parameters from
DTML docs. I've got an external method (original signature):

    def pfadleiste(self, pfadleisten_info, cut_last_entry):
       "..."

calling it via 

    <!--#var "pfadleiste(self, info, 0)"-->

is no problem at all, but if I change the signature to

    def pfadleiste(self, pfadleisten_info, cut_last_entry=1):

calling the same page in an identical context gives one of these darned
screwed-up "TypeError: read-only buffer, class" error that unluckily
hide
the original exception (a permanent pain when debugging -- if this
changes with the new Zope version it would be a reason for me to upgrade
even my existing system).

Stefan