Index: core.js
===================================================================
--- core.js	(revision 5458)
+++ core.js	(working copy)
@@ -1185,22 +1185,18 @@
 	},
 
 	map: function( elems, callback ) {
-		var ret = [];
+		var ret = [], value;
 
 		// Go through the array, translating each of the items to their
 		// new value (or values).
 		for ( var i = 0, length = elems.length; i < length; i++ ) {
-			var value = callback( elems[ i ], i );
+			value = callback( elems[ i ], i );
 
-			if ( value !== null && value != undefined ) {
-				if ( value.constructor != Array )
-					value = [ value ];
-
-				ret = ret.concat( value );
-			}
+			if ( value != null )
+				ret[ ret.length ] = value;
 		}
 
-		return ret;
+		return ret.concat.apply( [], ret );
 	}
 });