That would imply the emulated Intel NIC has some kind of problem when used with Windows 8.1 then (or that the NIC driver in Windows 8.1 has problems when used with an e1000e). Thank you, this is a good workaround for me, in that I always use guests with VMware Tools installed.
I may have been wrong about differences in IPv6 before. I had thought I had seen PING responses showing IPv6, but restoring the old e1000e setting I still see IPv4 responses, and I see IPv4 from my Windows 8 VM as well.
-Noel