Horn on FT - delayed violation?

[bgtg19]

The other thread ("New Interpretation") reminds me of a discussion we had in our area. This is the scenario. A1 is at the FT line to shoot one shot after a made basket and foul. After the ball is in A1's hands, the horn sounds as B6 reports to the scorer's table. Seeing that A1 is disconcerted by the horn, the lead steps into the lane to take back the ball, reset, and start the FT process again. B1, seeing the lead official stepping into the lane and knowing/thinking that B6 is reporting to replace him, leaves his assigned spot in the lane and heads toward the bench. When B1 leaves, the ball is still in A1's hands. Official then takes the ball from A1, tells B1 he must stay in the game and get back in his assigned lane position. A's coach gets up hollering to get the officials' attention. Lead official goes to A's bench and explains to coach that because the horn disconcerted his shooter, he's resetting the FT. Team A's coach insists that it is fine with him, BUT that because B1 stepped into the lane while A1 had the ball, it is a violation (coach didn't say delayed violation, but you can't expect coaches to be precise....). As a resut, says Team A's coach, A1 should get his FT attempt and, if he misses, he should get another. Lead official says "We're not doing that coach. I stepped in to reset and we're resetting and playing on."

How do you think the rules apply to this particular situation?

(By the way, the main "teaching point" we seemed to agree on in our discussion was that if you are going to step in and reset any FT situation, always blow your whistle first. That way, there won't/shouldn't be arguments about actions after the whistle blows.)