I keep seeing these kinds of issues with ffd/rew. All the seeking (jumping around) is loading the CPU to 100% and there's none left for the UI thread to handle the button-up message.
Maybe Peter or one of the other staffers on here could try adjusting the settings near the top of LACF, to increase the time between seeks. Maybe also increase the initial jump size so the "effective velocity" is the same.
The timings I picked were based on what sounded best, but if the CPU ain't fast enough - tough luck!