Windows 8 > Elan touchpad: how to enable settings via registry?

Question

For some unfathomable reason, the control to modify scroll speed/sensitibity under control panel > mouse > ELAN is greyed out. Go figure.

I know where ELAN lives in the registry, but cannot figure out which entry to tweak in order to enable this control.

Does anyone know!?

[Edit: have already tried reinstalling driver; no dice...]

Answer 1

OK so after some help on TechPowerUp a poster notice something in an Acer forum that fixes the problem:

Under control panel > mouse properties > ELAN tab, hit 'options' and go to the third tab, 'additional'. Click 'gesture effect' in the left list.

Change from ZoomPerfect to Microsoft Modern Touchpad Experience.

Et voila! God alone knows why ELAN would disable such fundamental controls to start with...