Increase/Decrease game speed via hotkey not working

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.