you seem to be sending an empty list -- check if this is the case with an explicit 'list' message. This is usually a synonim for 'bang' (e.g. if sent to a [print]), but not always (e.g. not for a [v], which ignores it).
wait ... if i understand it correctly, a bang is represented by either an empty list or a "bang" message, the function class_addbang is only working for the message bang... "print" is also using the class_addlist function that's working for empty lists, too...
for me that's a bug in the _language_ pd ... since it can take hours to figure that out ...
anyway, thanks for the explanation ... tim