I have increase/decrease game speed rebound to page up/down (instead of ctrl+pgup/pgdn). When pressed, the game will increase/decrease speed by 5% as shown on the screen in text, however it won't increase/decrease further.
ie. Speed = 100%, press page-up, speed shows 105%, press page-up, speed shows 105%.
Adjusting the game speed via the settings menu works fine though.
Customer support service by UserEcho