- disable re-tesselating derived meshes in BMEdit_RecalcTesselation() have modifier stack do this.

- made editbmesh_calc_modifiers() ensure tessfaces, this has the advantage that if the tessfaces are already created they wont get re-made as was happening before.

source/blender/blenkernel/intern/DerivedMesh.c

@@ -1776,7 +1776,12 @@ static void editbmesh_calc_modifiers(Scene *scene, Object *ob, BMEditMesh *em, D
 		(*final_r)->calcNormals(*final_r); /* BMESH_ONLY - BMESH_TODO. check if this is needed */
 	}
 
-	DM_ensure_tessface(*final_r); /* BMESH_ONLY */
+	/* --- */
+	/* BMESH_ONLY, ensure tessface's used for drawing,
+	 * but dont recalculate if the last modifier in the stack gives us tessfaces  */
+	DM_ensure_tessface(*final_r);
+	if (cage_r && (*cage_r != *final_r)) DM_ensure_tessface(*cage_r);
+	/* --- */
 
 	/* add an orco layer if needed */
 	if(dataMask & CD_MASK_ORCO)

source/blender/blenkernel/intern/editderivedmesh.c

@@ -223,6 +223,8 @@ void BMEdit_RecalcTesselation(BMEditMesh *em)
 {
 	BMEdit_RecalcTesselation_intern(em);
 
+	/* commented because editbmesh_build_data() ensures we get tessfaces */
+#if 0
 	if (em->derivedFinal && em->derivedFinal == em->derivedCage) {
 		if (em->derivedFinal->recalcTesselation)
 			em->derivedFinal->recalcTesselation(em->derivedFinal);
@@ -233,6 +235,7 @@ void BMEdit_RecalcTesselation(BMEditMesh *em)
 		if (em->derivedFinal->recalcTesselation)
 			em->derivedFinal->recalcTesselation(em->derivedFinal);
 	}
+#endif
 }
 
 void BMEdit_UpdateLinkedCustomData(BMEditMesh *em)