Jog Wheel functions

Why doesn't the jog wheel work the way I expect it to?

The jog wheels and tempo sliders don't work while Merge FX is turned on when I'm using Serato DJ Pro. Why not?

I can't scratch.

Backspin continues even after the jog wheel stops when I'm using rekordbox.

What is Jog Cutter? (Serato DJ Pro)

What is Jog Cutter? (rekordbox)