Compiz and Desktop Wall

[Fred Williams]

After a fresh install of F12, and enabling the 3D graphics correctly, I
activated Compiz and the desktop wall - however, unlike usual, using the
scrollwheel on the desktop doesn't scroll through the different
workspaces.
There's probably something I've overlooked in the Compiz control panel,
or more likely someplace else, but wherever it is, it's hiding and
laughing at me.
How to get this one thing back?
Thanks.