Uses a copy of the flags when they are given as an object rather than the...

Uses a copy of the flags when they are given as an object rather than the object itself. That way, we're sure flags are immutable for the entire lifetime of the Callbacks instance.

src/callbacks.js

@@ -40,7 +40,7 @@ jQuery.Callbacks = function( flags ) {
 
 	// Convert flags from String-formatted to Object-formatted if needed
 	// (we check in cache first)
-	flags = typeof flags === "string" ? ( flagsCache[ flags ] || createFlags( flags ) ) : ( flags || {} );
+	flags = typeof flags === "string" ? ( flagsCache[ flags ] || createFlags( flags ) ) : jQuery.extend( {}, flags );
 
 	var // Actual callback list
 		list = [],