I just did some further experiments and determined that the problem was that I'm not waiting long enough! Despite getting a 'opengl conversion 100%' message in Bryce it seems that some internal processing still has to take place and that simply minimising the program (it doesn't seem to happen whilst it's onscreen) and waiting 10 minutes or so is enough for the program to 'wake up' and display properly in OpenGL. I've found this also occurs with large textures (say 2000 pixels square) even when applied to a 2d square directly in Bryce. Darlissa did mention something about waiting several minutes for the OpenGL conversion process but I thought she was referring to the actual import. It seems that for some of us at least that the OpenGL display in Bryce 5.5a is far more spotty than it should be, especially considering how comparitively well it works in Studio. I guess if you've got more complex scenes it's OK to wait for the OpenGL to 'kick in' but for me it's quicker in many cases simply to do an actual render before I can get a decent OpenGL 'preview'.