Well, the server will not accept anything after the "?", so that is moot. Also, I tried alternating the timer with a plain empeg_screen.png and one followed by a ?. No luck.

At this stage, I think the browser is still caching the image somehow, and having two instances of the browser is forcing the issue by being slightly out of sync. One interesting note is that IE7 tabs display two different screen images, but neither refresh.