CentOS - Sep 2014 - Screen refresh seems to fail until I move the window

Hi List,
Over the last month or so I have noticed a problem that seems to be 
becoming more noticeable.
Initially I noticed this on Thunderbird and Firefox and assumed (yeah 
that makes an ass out of u and me) it was related to mozilla updates to 
these products. As I was working mainly with email and the browser, I 
did not notice it also affects other products.

What happens is this: I delete an email, initially nothing changes on 
the screen, in fact the screen only updates if I do any of the following 
(not an exhaustive list)
press the down arrow to move onto the next email
click on the title bar and move the window
move the mouse to the bottom pane and use the scroll wheel - this will 
update this pane to the next email content, but fails to update the 
email header pane
click on some other folder
etc.
OR
working in gedit with multiple tabs (files) open. click to close a tab - 
nothing happens until I click on the title bar and move the window, or 
click onto another tab and then scroll in the edit pane ....
OR
working in firefox, and a pop up dialog box opens, the screen locks but 
no dialog box visible until I move the window slightly, when it does a 
screen refresh and greys out the main window and reveals the pop up box.

Running on CentOS 6.5, fully up to date as of Sunday, with nvidia 
graphics using the kmod packages from elrepo.
I also use compiz as my ASUS GT640 PCI-E 2GB graphics card has lots of 
horse power and run two 22" monitors via DVI cables from the single 
graphics card.
Not sure what else is relevant
Not a show stopper, but starting to really bug me.
TIA for any ideas.
Rob