Manuel and Chris,
It looks like there may be a viable patch to fix this issue posted on the pfsense boards. Could the same or a similar patch be integrated into monowall? While this issue has not yet effected any of our clients, I am nervous, thinking it is just a matter of time. Please see the link below for the pfsense board discussion and the patched code.
http://forum.pfsense.org/index.php/topic,7248.0.html[Looks like Manuel is already aware of this issue and has created a fix based on the last few postings in the link above. My guess is that it will be included in the next version(s). Three cheers for Manuel!]