Never saw it called, saw a few times where by rule it should have been. There were a few kids that dropped a foot behind the 35 after the RFP, but got back in place and set before the kick, so they gained no advantage.
Had another where the soccer style kicker took his steps back on an angle, which temporarily put only 3 guys one side of the "kicker". Again, no advantage was gained, because when the kicker moved forward, the situation was corrected before the kick.
By rule, both of these were fouls. In practical application, they shouldn't be. It just proves that while I dislike the actual rules and don't think they were necessary, even if they should be there by philosophy, the wording is absurd.