Sure, port mapping woudl work for things like SSH, but I just didn't want the hassle.
I'm thinking the issue might be IP Routing that I had turned on a while back for another experiment, and now am having a hard time turning it off. I have all 3 registery entries for IPEnableRouter set to 0, yet after a reboot ipconfig /all still shows IP Routing Enabled: Yes . So that's a bit of a mystery. This shouldn't be an issue, i.e. Windows should know in the bridged case that both IPs are on the same network and no forwarding is needed, but who knows... The fact that I can't seem to turn it off is an indication that something is futzed up!