Is this very common? Because that would certainly explain the behavior I see in games like WoW where turning my camera drops the framerate, but once I stop turning the framerate jumps back up to normal. I always assumed this had something to do with loading textures or models or geometry or something, but I was never really satisfied with that.
Your assumption was right. The choice of sort is purely an optimization to allow for fast depth-culling, and shouldn't result in noticeable graphical glitches. However, pipelining textures and models based on viewing angles is common. This is certainly what you are seeing.
