F4 fullscreen Mac not working

Hi, I'm a Fusion noob coming from Nuke.
According to the user guide, the F4 key will make the window under the cursor full screen - just like the SPACE bar in Nuke.
Yet it doesn't work on my computer... All other Function keys work correctly...
Any ideas what's wrong?
I'm dying a slow death without that function please help ;0)
Thanks, Konrad

There's a subforum for beta issues.