I have not heard of this behavior before. This could be something related to graphics card or driver version. Look at the Platform Support page and make sure that the graphics card and driver version are listed as supported or certified.
In the By Product drop down select the release you are using, e.g. PTC Creo 3.0.
I *think* I have seen this before. It's very random and only happens occasionally, maybe only once a week. As originally posted, sometimes it's regeneration but I think it's also sometimes on save. Definitely not reproducible or at least what I have seen is sporadic. I'm on Creo 3 M070.
Steve Williams Pro/E Version 15/16 (Circa 1995/1996)