Ethernet internet sharing/bridging fine on Win 7, not on 8.1

This is a strange one. I have an ethernet sketch that works fine on a windows 7 laptop with a bridged ethernet/wifi setup. I plug it into a windows 8 machine with an identical setup and nothing. Doesn't even get assigned an IP by the DHCP.

I've tried a combination of settings, including manually setting IP/DNS on the Uno, tried both the webclient example sketches but cannot get it to connect.

If i plug another laptop into the 8.1 machine to test the bridging it works fine, DHCP and everything.

Anyone else come across this quirk?