Spacebar is a key used for accessibility on Windows (and other platforms). By defeault, if a button has focus, the pressing the spacebar will active the button. This is problematic because in the ROLS tuning application spacebar is used to clear the step scale.
The Alt key is used on Windows (and other platforms) to access the applications menu bar. So there is a conflict between this OS buildin behavior and using the left/right Alt keys to change the step scale.