I use a unicomp keyboard, and I have the same problem. I think the problem is that it draws quite a lot more current than other USB peripherals. I have mine plugged into a powered USB hub, which seems to help.
It definitely pushes the envelope on power, if it's connected to a port that doesn't deliver, it won't work right... much more than typical membrane keyboards. They also have issues with some KVM switches that don't provide enough power. Wound up using a split power cable (like one that's usually for extra power to USB external drives, so I could push extra power into the USB interface.
Love the keyboards though... despite some QC issues.
Love the keyboards though... despite some QC issues.