It actually hasn't before, not that I can see :0...huh.
I don't think there is a way to make parrallax work as it would require multiple assets to get it to work(?) it starts approaching that 3D territory pretty fast, sorry ><
This is probably the rule that covers it:
ONE BACKGROUND
It is within the rules to:
- use layers to show a sliced up an image as a single background (no opaque parts of layers can overlap)