Alt-tab switching weirdness

[Tony Whitmore]

I've been experiencing some odd behaviour from the Alt-tab application 
switching function of XFCE for the last few days.

For example, on one head I have Bluefish (the HTML editor) and a Firefox 
window. I'm editing code in bluefish and switching to FF to view it 
using Alt-Tab.  The odd behaviour is this: The Alt-Tab function has 
stopped passing focus back to the application being switched to. On 
hitting Alt-Tab the small window appears in the centre of the screen and 
toggles through the applications on that screen. Letting go of Alt-Tab 
does not bring the last shown application into focus however. The 
Alt-Tab window remains on screen and nothing happens.

The mouse is able to move around that screen, but not outside it. It is 
unable to interact with any of the items on the screen. The keyboard is 
able to interact with the application in focus, i.e. if Bluefish was in 
focus before I hit Alt-Tab, I can continue to type into the Bluefish window.

After a seemingly random number of hits of Alt-Tab, the Alt-Tab window 
will disappear and the last application shown will be brought to the 
front and given focus. I'm pretty sure that no keys are being stuck 
down, and this only seems to happen on one head of the two. I have 4 
virtual desktops on that head and it seems to happen on all of them. 
I've not experienced this problem on the other head, nor on my laptop 
which runs the same packages and roughly the same configuration.

I have a dual head setup (not Xinerama) using two monitors running at 
1280x1024 on an ATi Radeon 9200, on a Debian Sarge system using XFCE 
4.2.1 from osworks.com. I use a focus-follows-mouse configuration.

Has anyone experienced similar or could offer me any tips?

Thanks,

Tony Whitmore