It means the menu option that lets you skip innings. It also includes the time when your player isn't active during RTTS.
Basically, anytime you're looking at the screen with the diamond view, lineups and the scrolling summary of what's going on, that's fast-forwarding. Obviously, a bug like this would have a large impact on RTTS, as it hits whenever the game comes out of that screen to let your player do his thing.