The issue #6099 (part of #6267 superset) introduced a regression:
xmlrpclib.make_connection() is not thread safe. If xmlrpclib is used in two
threads, the socket is shared, but it doesn't any lock, and so data will be
mixed between the two requets. It becomes worse when I use SSL (pyopenssl
or m2crypto).

A possible solution is to use a different socket for each thread.

Note: I really love #6099, it was exactly what I needed :-)