Is this the Wilkinson with the trem-lockdown in neutral? There may be a malfunction with this....or, is the bridge plate is too close to the top of the guitar, rotating the arm will cause the bearing edge to slip away from the grooves in the fulcrum posts. You may need to shim the neck back, just a bit..then raise your tailpiece a hair.
And, it could just be a defective unit...it happens.
