A different way to fix (faster, not computing normalMatrix).

src/renderers/WebGLRenderer.js

@@ -706,7 +706,7 @@ function WebGLRenderer( parameters ) {
 
 	this.renderBufferDirect = function ( camera, fog, geometry, material, object, group ) {
 
-		var frontFaceCW = ( object.isMesh && object.normalMatrix.determinant() < 0 );
+		var frontFaceCW = ( object.isMesh && object.matrixWorld.determinant() < 0 );
 
 		state.setMaterial( material, frontFaceCW );
 

src/renderers/webgl/WebGLShadowMap.js

@@ -383,7 +383,6 @@ function WebGLShadowMap( _renderer, _objects, maxTextureSize ) {
 			if ( object.castShadow && ( ! object.frustumCulled || _frustum.intersectsObject( object ) ) ) {
 
 				object.modelViewMatrix.multiplyMatrices( shadowCamera.matrixWorldInverse, object.matrixWorld );
-				object.normalMatrix.getNormalMatrix( object.modelViewMatrix );
 
 				var geometry = _objects.update( object );
 				var material = object.material;