Hi 

I have the same problem and contacted the poser support. After a lot of suggestions with no results they closed the ticket. This problem tunes my nuts. It is defenitely a bug, because Poaser 11 pro does it not!! I believe it has to do with the texture cache. Poser 13 loads all textures again and again if you switch between rendering and working screen.

I hate it...sometimes more than 30 seconds:-(