ObjectLoader: fix duplicate materials

src/loaders/ObjectLoader.js

@@ -497,8 +497,13 @@ Object.assign( ObjectLoader.prototype, {
 
 				} else {
 
-					materials[ data.uuid ] = loader.parse( data );
-					cache[ data.uuid ] = materials[ data.uuid ];
+					if ( cache[ data.uuid ] === undefined ) {
+
+						cache[ data.uuid ] = loader.parse( data );
+
+					}
+
+					materials[ data.uuid ] = cache[ data.uuid ];
 
 				}