try this...
hold ball with hand, fingers and thumb in the holes.
palm face upwards, so the weight of the ball resting on ur
palm.
use the other hand as a support, try to get the ball out from thumb
while keeping fingers in inserts still. does this test help to see
if the thumb can get stuck or what?
The second one is on knees, swing ball lightly. On the
backswing(slight), release the ball with the thumb first and try to
lift with fingers.

i dunno about these tests.....just saying cos i use it. haha