hmmm, the add to bid is working with that code in both IE8 and FF for me without any issues, it even brings up the "already in bids" if you hit it more than once.
I am guessing that the popup login is something using javascript that was added after the original install, almost sounds like it may be suffering the from the same issue as the javascript for the map and add to bids...... maybe it is the cause of the issue and is conflict with the newer phpvms coding..