I have owned two of these units, one I just purchased last weekend and I have had no problems with X1 like you are describing with this unit or the one I owned 2 years ago on a completely different system and running Sonar 8.5. I am running Win 7 64 bit on an AMD Phenom 6 core with Sonar X1c Expanded.
So a few questions:
-are you running the lastest driver update and is it the 64 bit version?
-did you have a previous soundcard or a previous version of the Ua25ex driver installed?
-are you using a wireless mouse?
-have you tweaked Win 7 in any way?
-do you have antivirus on the computer?
-do you have the onboard sound switched off in BIOS and is the driver removed as well?
-have you tried installing the unit on another computer to see if this happens on another system?
Any one of these things can cause problems and ther are tons more reasons that this could be happening but you need to provide a bit more info and you need to make certain that the unit does the same thing on another computer. That will be the only way to be certain that it is the unit and not the computer causing this problem.
One thing to try is using the WDM/KS. I have found flawless performance with this over the ASIO. I can get 2ms latency across 24 or so VST tacks and have no problems at 48/24.