I'm willing to bet something going wrong with fragment reassembly on
one end or the other..

Have you looked at:
	- tcpdumps of the traffic 
	- the size of the reassembly space..
	- netstat -s -p ip output to see how the
	  fragmentation/reassembly is doing?

one or more of these may point more precisely at the problem...

then again, "fragmentation considered harmful"..  

					- Bill