Index: event.js
===================================================================
--- event.js	(revision 4750)
+++ event.js	(working copy)
@@ -321,8 +321,8 @@
 		}
 			
 		// Add which for key events
-		if ( !event.which && ((event.charCode || event.charCode === 0) ? event.charCode : event.keyCode) )
-			event.which = event.charCode || event.keyCode;
+		if ( typeof event.which == "undefined" && (typeof event.charCode != "undefined" || typeof event.keyCode != "undefined") )
+			event.which = typeof event.charCode != "undefined" ? event.charCode : event.keyCode;
 		
 		// Add metaKey to non-Mac browsers (use ctrl for PC's and Meta for Macs)
 		if ( !event.metaKey && event.ctrlKey )