Hi Flamingo!
I don't know the cause, would have to leave that for the developers :) Just wanted to have as much information as possible on how and when this happens, as that can sometimes be critical to finding out what is going wrong, ty for that!
I've not been able to duplicate it here so far, also using R19 on a PC, with Display set to Gourad Shading. Is it every scene and every material by the way? Corona Materials, and does it make a difference if they have bitmaps applied, or bump mapping, etc?