Well, this morning I have been testing out a theory and, so far, I am able to share the same ssh and vnc ports without Virtual PC 6.1.1 kicking me off.
I changed the networking preference for VPC from Shared Networking (where the Mac and the Windows virtual machine both share the same tcp/ip address) to Virtual Switch where the Windows virtual machine gets its own separate tcp/ip address.
Don’t know why it helped (or maybe the sunspots are less today) but it seems to be working fine.
Just an FYI.