USB mouse via PS2 KVM works when 2nd USM mouse plugged in

Odd behaviour. IOGear PS2 KVM 2-port built in cables.

USB MS optical wheel mouse using its included USB->PS2 adapter.
With Vista x32 Business with SP1, I have no issues. The setup works as
expected.

But with Vista x64 Ultimate with SP1, the mouse via the KVM mouse only
works if I have a 2nd USB mouse plugged directly into the PC while Vista
boots up. After it's booted, I can unplug the extra mouse and the PS2
KVM mouse will keep working. BUT if the USB mouse is not connected when
I boot Vista, then the PS2 KVM mouse does not work.

Fresh install of Vista Ultimate x64 with SP1 and all windows updates. I
want to solve this before I start adding my software.

As of right now, I only know of 3 possible solutions.
1. Leave a spare USB mouse plugged into Vista x64 all the time and wrap
it up behind the PC. Lame, but that's what I am doing right now.
2. Buy a USB based KVM. I really don't want to spend the money on that
since option 1 above is working at no extra cost to me.
3. Buy a different PS2 based KVM to test with. Again, don't want to
spend the money.

Also, seems silly to buy another KVM when the one I have works fine
with x32 Vista and only has this oddity with x64 Vista, yet it does work
in x64 Vista with the spare USB mouse plugged in at boot up and can be
removed after bootup. So it seems there should be a software solution to
solve the issue.