I don't know if this relates to the problem OP described.
I have two 15-year-old Belkin 4-port KVM switch -- which, of course, uses PS/2 connections for mouse and keyboard, and your usual 15-pin VGA analog plugs for video. These old Belkin units cost me nearly $200 a pop when I bought them. They have been very reliable, but I don't have DVI.
Now the latest snag in my upgrade plans -- My Z68 motherboard didn't come with PS/2 ports, and it was the one thing I overlooked in ordering it. So I picked up a PS/2-to-USB converter cable. Seemed to work fine. the Z68 is running Win 7 Pro 64-bit.
And it continues to "work fine" -- with some minor glitches that seem manageable. When I switch back to the Z68 from another computer, the mouse cursor seems to go haywire for a moment. It will open "desktop properties," mess with my Windows 7 gadgets, and so on before it "settles down." I've learned to manage it: I position the mouse cursor on unused desktop space, right-click it to take focus away from running programs, and then switch the KVM to another computer. When I return, I've found it is best to wait for a second before moving the mouse.
I can't tell if this is some "tantrum" that USB plays with the Belkin, or if it isn't just a peculiarity of USB keybd and mouse devices.