I tried playing it yesterday, and wasn't able to duplicate the problem. I wondered if I wasn't precisely repeating what you did.
Were you using a cheat code while it happened? I know that Vern has some code in place to degrade some of the graphics effects if frame rate goes down for a while. I'm unsure of the extent of this degradation, but I'm pretty sure it wasn't meant to be as extreme as this. It does generally fit in with what you're seeing since it doesn't happen immediately.
It could be related I suppose. It also looked like a few of the tiles were a little messed up in that image. We saw it in some of the original mansions as well when converting them for the new game.