I haven't heard of this being an issue before on LTM. Are you able to reproduce the issue if you use a client and connect directly to one of the Exchange servers?
Here is a related thread with some MS KB links that might help:
http://social.technet.microsoft.com/Forums/en-US/exchangesvrgeneral/thread/84de4213-a532-45da-b9c7-6fba8f4efb9a
If you do think it's an LTM issue, I'd suggest capturing tcpdumps on the ingress and egress VLAN(s) to try to determine exactly what's happening. If you need help capturing or analyzing tcpdumps, you can search the forums or AskF5.com for details, or open a case with F5 Support.
Aaron
Nimbostratus
