When to hold up a trump winner

Bryan wondered: If, as defender, you have the ace of trump, and declarer starts pulling trump, is there any situation when you wouldn't want to win with your ace on the first round?

My instinct was yes, of course there is, but I couldn't think of one in the heat of the moment. On reflection, though, I whipped up a quick example. Tell me if you find a flaw.

Contract: 4   
Lead:  3

North

 5 4

 K 8 2

 K 10 5 3

 Q 9 7 5

West

 K 9 7 3

 10 9

 Q 8 7 4

 A 10 8

East

 Q 10 6

 A 7 4

 J 9 6

 J 4 3 2

South

 A J 8 2

 Q J 6 5 3

 A 2

 K 6

South wins the spade lead in her hand and starts to pull trump. If East wins with the ace, he can return a spade to West's king. The club ace will be the defense's third and last trick.

However, if East ducks the trump lead, it puts declarer at a disadvantage. When East wins the next round of trump, he can lead his last trump, removing the dummy's ability to ruff a spade, and giving the defense another eventual spade trick.