Picture problems with very bright images

I have an older CRT-based Mitsubishi HDTV. I have recently been experiencing problems with the picture when very bright images, such as a picture which is mostly white, or images mostly of the sky, etc. are displayed.

The picture will break up and the screen will usually black out until a less bright image is displayed. The majority of the time, the picture is fine, but if the image is very bright, the problem occurs.

I have kept my TV calibrated using DVD Essentials, but when I recently checked the settings, due to the issues I was experiencing, it appears that the settings went back to the defaults. The Contrast was maxed out and the settings were all wrong.

I have since backed down the contrast and readjusted the settings, but the problem still occurs (maybe a little less often, but not much).

I guess I have a few questions about this...

1) Can anyone explain why this is happening?
2) Is it likely that my set is permanently damaged? If so, can it be fixed and what is it likely to cost?
3) Is it time to look for a new TV?

Any input would be greatly appreciated.

Thanks!