..but wouldn't I experience freezing's also in regular games (or when I run project from WED) if the problem is DirectX related? I don't know, I may be wrong with the openGL theory.

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Update: I can also fix freezing with RightClick->GXL->Refresh/Recreate Views. But the strangest thing of all is that freezes seem to be happening only when bigger groups are selected?? Is this possible? Did anyone ever had similar problem? I can make a small video to demonstrate this.