Ah, that one...you have this problem in the older AWTGLRenderer version too. I've already noticed it at exactly the location in the video and near the door of the starting room. It's a z-bufferering issue caused by the planes of the objects' triangles lying into each other (or at least they are very close). The flickering can have many reasons, for example inaccuracies in the vertex calculations when transforming the vertices into camera space, different rendering order (not very likely, but possible) or plain and simple inaccuracies in the z-buffer and/or the z-buffer optimizations the GPU performs. In similar situations, one can very well see the tile structure in which the ATI chips are rendering the picture due to such inaccuracies.
Changing the z-buffer's depth won't help here. The only solution is a geometrical one: Avoid that it happens when creating the scene. As long as two or more triangles' planes are lying into each other and the triangles overlap, you'll always see such artifacts. They may differ from hardware to hardware, but the basic problem remains.