Index: src/fx.js
===================================================================
--- src/fx.js	(revision 4843)
+++ src/fx.js	(working copy)
@@ -69,8 +69,10 @@
 		return this.animate({opacity: to}, speed, callback);
 	},
 	
-	animate: function( prop, speed, easing, callback ) {
+	animate: function( prop, speed, easing, callback, changeOverflow ) {
 		var optall = jQuery.speed(speed, easing, callback);
+		// default value of change overflow is true
+		changeOverflow = typeof(changeOverflow) == "undefined" ?  true : changeOverflow;
 
 		return this[ optall.queue === false ? "each" : "queue" ](function(){
 			if ( this.nodeType != 1)
@@ -92,7 +94,7 @@
 				}
 			}
 
-			if ( opt.overflow != null )
+			if ( changeOverflow && opt.overflow != null )
 				this.style.overflow = "hidden";
 
 			opt.curAnim = jQuery.extend({}, prop);