I think I found two possible bugs:
After calling ent_setmesh and manually setting min/max values, the entity is still clipped using the size of the old mesh. For example I have an 8x8x8 box (4 vertices) and I call ent_setmesh to change the mesh to a large terrain (128x128 vertices), the terrain is clipped when the 8x8x8 box is not visible.
Also, ent_setmesh does not work on terrain entities...?