I don't know the specific problem which you are having, however I have run into something similar once before. On a previous build one of my PCs (an nForce4 motherboard iirc) had a problem when it was directly connected to a KVM. For some reason the KVM and motherboard USB controller did not get along, so it would continually connect/disconnect/connect/...
The solution which I read somewhere was quite simple - take a cheap USB hub and plug that into the motherboard, then plug the KVM into the hub. Simply having the hub between the motherboard and the KVM was sufficient to calm everything down and it has worked perfectly since (in fact I still have that USB hub ziptied to the back of the problem machine). If indeed the keyboard USB is causing a problem you might try using a cheap USB hub like that to see if it fixes it.
Other option if you have a PS/2 port available is to convert the Deck to PS/2 and use it that way (conversion instructions are in the manual: http://www.deckkeyboards.com/documents/legend_usermanual.pdf