8-stable crashes in vmware (possible em driver issue?)

[Ivan Voras]

I have a fairly recent 8-stable machine running under VMWare ESXi 3.5 
(amd64 guest), which apparently crashes every few days from the same causes:

em0: discard frame w/o packet header
em0: discard frame w/o packet header
em0: discard frame w/o packet header
Panic string: sbsndptr: sockbuf 0xffffff007cca8c20 and mbuf 
0xffffff00490a6400 clashing

More information available here:

http://ivoras.net/stuff/crash/info.0.txt
http://ivoras.net/stuff/crash/core.txt.0.txt

The crash looks like is provoked by ssh bruteforce attack attempts, some 
of which are blocked by an ipfw-based blocker.

Any ideas?

The machine was previously (until a month ago) running 7.2-RELEASE 
without these panics.