This is the play-by-play recap of the Saints' final offensive possession against the Lions:

New Orleans Saints at 3:03

1-10-DET 33 (3:03) C.Ivory right guard to DET 31 for 2 yards (S.Tulloch; J.Durant).
Timeout #2 by DET at 02:57.
2-8-DET 31 (2:57) C.Ivory right end pushed ob at DET 30 for 1 yard (A.Spievey).
3-7-DET 30 (2:50) (Shotgun) D.Brees pass incomplete deep right to M.Colston.
PENALTY on DET-A.Berry, Defensive Pass Interference, 23 yards, enforced at DET 30 - No Play.
1-7-DET 7 (2:44) PENALTY on NO-J.Evans, False Start, 5 yards, enforced at DET 7 - No Play.
1-12-DET 12 (2:44) C.Ivory left guard to DET 2 for 10 yards (N.Suh; K.Vanden Bosch).
Two-Minute Warning
2-2-DET 2 (2:00) D.Brees kneels to DET 3 for -1 yards.
3-3-DET 3 (1:20) D.Brees kneels to DET 4 for -1 yards.
4-4-DET 4 (:38) D.Brees kneels to DET 5 for -1 yards.

Question: Why didn't the clock stop immediately following Brees's 4th down kneel? This was technically a change of possession, yet the clock was allowed to run out. Not that Detroit could have possibly mounted a 17 point comeback from their own 6 yard line with 36 seconds left. I'm just curious as to why this occurred. Was some little known mercy rule enforced?