With the current language, there is the distinct possibility of a team gaining a huge advantage - like winning the game - by having a helmet come off during the last minute of a half. Since the play clock is to set to 25 seconds, regardless of which team has the helmet come off, the team behind can force the team ahead to run a play when they might have otherwise been able to let the game clock expire.
A=22, B=20, 3/10, A-25, 4th period. A11 gains 4 yards and is tackled with the ball becoming dead in the field of play. As A11 is being tackled, the helmet of nearby B33 comes off and the clock is stopped accurately with 0:39 on the game clock. B33 is sent off the field and A accepts the 10-second subtraction, taking the clock down to 0:29. The play clock is set to 25 seconds, and the ball is made ready for play for 4/6, A-29. Both clocks are started correctly, and A snaps the ball with 4 seconds on the game clock. A11 muffs the snap, which is recoverd by B55 at the A-28, with 0:02 on the game clock. B takes over and kicks a field goal as time expires to win the game.
Those are circumstances approaching the extreme, but far stranger things have happened. I suppose a team that can't burn four or five seconds off the game clock doesn't deserve to win. But, it doesn't seem quite right to allow a team to be put in that position by the possibly deliberate illegal action of an opponent.