Try the attached zip.  In GZdoom 1.0.32, and all other official versions supporting models and it looks like a healthy clump of grass from all angles.
Load it into r10 and as you move around it, parts of it disappear.  The model is just a very simple criss-cross of flat surfaces with a simple skin attached to them - a very common technique for making trees, signs, etc etc.
			
			
									
						
										
						r10 Models with flat planes not rendering from all angles.
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