mleghorn
When I use Dimension Pro with X2, every time I hit a note an any patch that has a long decay, the note sustains indefinitely. I don't have this problem with other VSTs & X2.
Most keyboards don't send MIDI off messages any more - they send 0 velocity or 0 volume note messages. I know that is beside the point - but may hold the key to your problem.
Have you looked in the event view to see what's actually happening?
Brian