Here's the rule:
ART. 3 . . . An inadvertent whistle ends the down. Inadvertent whistles are administered as follows:
a. The down shall be replayed if, during a down or during a down in which the penalty for a foul is declined, an inadvertent whistle is sounded while a legal forward pass or snap is in flight, or during a legal kick.
b. The team last in possession may choose to either put the ball in play where possession was lost or replay the down if, during a down or during a down in which the penalty for a foul is declined, an inadvertent whistle is sounded while the ball is loose following a backward pass, fumble, illegal forward pass or illegal kick.
c. The team in possession may choose to either accept the results of the play at the dead-ball spot or replay the down if, during a down or during a down in which the penalty for a foul is declined, an inadvertent whistle is sounded while the ball is in player possession.
d. The penalty shall be administered as determined by the basic spot and takes precedence over inadvertent whistle administration if, during a down, a live-ball foul occurs prior to the inadvertent whistle and the penalty is accepted.
You keep seeing the clause "during a down in which the penalty for a foul is declined...." If there is an IW in a play where there is a flag, the IW is ignored as soon as the offended team accepts the penalty.
A play in my game a couple years ago. K punts. R signals for a fair catch but a player from K bump into him just as the call get there. The ball goes through his arms and bounces loose. During the scramble my back judge blew his whistle, then felt terrible because of the inadvertent whistle. I said don't sweat it. The flag wipes it away. Enforce kick catching interference and move on.
