Magic trackpad gestures not working properly

Hi,

I have a late 2010 MacBook Pro, currently running Mountain Lion OS X 10.8.1.

The integral trackpad works fine, with all the gestures working.

But when I connected my MBP to my Cinema Display this afternoon, and ran it in clamshell mode using my wireless Keyboard and Magic Trackpad, I noticed that some of the gestures on the trackpad weren't working.

Well, specifically the four finger swipe to change between full screen apps doesn't. I wanted to get to dashboard to see why my fans seemed to be working so fast, but the four finger swipe wouldn't work at all. I had to resort to opening Dashboard from my apps folder.

The battery on my trackpad is showing at 99%, and it seems to be paired correctly, as is the keyboard.

Two finger swipe to page back and forth in Safari works fine, as do all the other gestures I've tested. It just seems to be the four finger swip that doesn't.

Any ideas anyone please?

Errr... and I've just discovered that, having made Safari full page, I can't get it to go back to normal by pressing Esc on the wireless keyboard. What is going on here?