If the cursor is twitching/jerking on its own, then it might be signal interference. A friend of mine had this issue with her old wacom after she moved... bought a new one, same problem. Finally a friend of hers brought their own tablet to her place, and it started giving the same symptoms. This friend then took the wacom and her machine home with her and the problem didn't occur, it was location specific.
Signal interference/EMI isn't that uncommon unfortuantely, but as Rob said contacting support is the best option. The Wacom people eventually ran out of things to try and concluded it was an EMI issue for the friend of mine, before she found a friend that could help prove the theory.
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