Odd graphics in periscope

[kurtz]

I occasionaly get a very odd effect in my periscopes and uzo.

The screen becomes partially filled with Jimi Hendrix coloured three quarter inch squares I don't have any problem until I try to use the periscope then it starts to appear everywhere. Exiting then coming back cures it but it is a bit irritating.

Any help appreciated I've got an nVidia card with 128Mb a 5800 i think not by my computer at the moment. The drivers are uop to date.

Mike