[X4U] screen flashes on&off

[Mary C. Youra]

My 13" MacBook Pro (10.5.8) sometimes, but not always, flashes on and  
off when trying to launch its screensaver (which I have selected as  
pictures from my iPhoto library). Hitting a key (any key) stops it,  
just as it would stop a screensaver. It's been doing quite awhile, and  
I used to think it had to do with having NetNewsWire active, but that  
proved not to be the sole cause, although it is usually running. So is  
Safari, but I can't say I've noticed a pattern about what else might  
be active. Because it doesn't happen all the time, I didn't pay that  
much attention to it. Fwiw, I did recently install the Security Update  
on this computer, and it did affect something with permissions, so  
that I now get some ACL notes that I was not getting before, of the  
kind that everyone says you can safely ignore, but clearly that has  
nothing to do with this behavior.

The reason for my note is that I also installed the Security Update on  
an iBook G4, same operating system (10.5.8). It has started to do the  
same flashing behavior while trying to launch the screensaver (Apple's  
Paper Shadow, not something custom). It never did that before. (Btw, I  
got the same three permissions ACL notes, which I thought curious.)  
This one, I can't blame on NetNewsWire, since it's not on that  
computer. Only Safari has been open and active, but it's occasional,  
not all the time.

My husband has an identical MacBookPro using pictures as a  
screensaver, but running Snow Leopard, and his does not do this.

--Mary Youra