LCD monitors can do this too - I have one system that does something like this most times it boots until the OS is loaded and the video driver started.

The option ROM on that video card isn't good enough at rejecting bad EDID reads and defaults to a video mode half the resolution that monitor can support. When the OS & its video driver take control they switch to the last video mode I used, which works.

Normally fried electronics can't sync at all, but that's not what happened to Susan with the web page stable on half the screen - it stayed in sync, with a wildly bad sync rate.