--- sites/resources/fitzwilliam/js/base/jquery.js	(revision 4808)
+++ sites/resources/fitzwilliam/js/base/jquery.js	(working copy)
@@ -4597,9 +4597,11 @@
             style.zoom = 1;
 
             // Set the alpha filter to set the opacity
-            var opacity = parseInt( value, 10 ) + "" === "NaN" ? "" : "alpha(opacity=" + value * 100 + ")";
-            var filter = style.filter || jQuery.curCSS( elem, "filter" ) || "";
-            style.filter = ralpha.test(filter) ? filter.replace(ralpha, opacity) : opacity;
+            if(parseInt( value, 10 ) + "" !== "NaN") {
+               var opacity  = "alpha(opacity=" + value * 100 + ")";
+               var filter   = style.filter || jQuery.curCSS( elem, "filter" ) || "";
+               style.filter = ralpha.test(filter) ? filter.replace(ralpha, opacity) : opacity;
+            }
          }
 
          return style.filter && style.filter.indexOf("opacity=") >= 0 ?