1) Yes, a bug. Can be fixed from the command line:
a) run polib:
> polib -machine:amd64 -makedef:temp ws2_32.lib
(this will create a text file called temp)
b) edit temp, add a second underscore at the beginning of WSAFDIsSet (_WSAFDIsSet --> __WSAFDIsSet), save modified temp.
c) run polib again:
> polib -machine:amd64 -def:temp -out:new_ws2_32.lib
(this will create new_ws2_32.lib which should replace ws2_32.lib -- but make a copy of ws2_32.lib for safety!)
2) I can reproduce it. Maybe I can fix it too.