I thought that I had heard cushion-contact rules once stated as, "IF a ball is not pocketed" which could be argued that a ball could be pocketed, and then un-pocketed, and it was fine--The thought being that after-contact with a cushion was not required, since the ball was pocketed. However, I could not find anything to back that up.
Ringing in for the non-pro rules, I did find that the APA has this (italics is mine):
7. POCKETED BALLS
Balls must remain in a pocket to be legal. If any ball, including the cue ball, goes in a pocket, but bounces back onto the playing surface, it is not considered pocketed and must be played from where it lies.
And this is under the 15.FOULS section:
c. Failure to hit a rail or pocket a ball after contact. A rail must be struck by either the cue ball or any other ball after the cue ball contacts the object ball. If the ball bounces back onto the playing surface, it is considered to have struck a rail.
