We only need to encode the keys.

celery/worker/control.py

@@ -122,5 +122,5 @@ class ControlDispatch(object):
         else:
             # need to make sure keyword arguments are not in unicode
             # this should be fixed in newer Python's (see: http://bugs.python.org/issue4978)
-            kwargs = dict((k.encode('utf8'), v.encode('utf8')) for (k, v) in kwargs.iteritems())
+            kwargs = dict((k.encode('utf8'), v) for (k, v) in kwargs.iteritems())
             return control(**kwargs)