[old_tv_nut]

It is not necessarily a problem. It mainly depends on the high voltage and focus voltage decaying more slowly than the video and sweep power supplies. I don't know how to tell you how to distinguish if your case is unusually long and bright, but if it hasn't burned a spot in the phosphor yet, it probably never will.

If you could post a video of it, someone might be able to take a guess as to whether it really is trouble or not.