Memory leak in Pl/Python

I have postgresql 9.4.8 on my server and I've noticed always growing
memory when I use plpython. I've made some tests and find a few
situations, when memory leaks. For example, when I call this procedure
many times, I can see an always growing memory:

create or replace
function test() returns bigint as $$

plpy.execute("insert into test(test) values ('test')")

return 1

$$ language plpythonu;

Interestingly, when I use not-modifying data query ('select 1') as
argument of execute(), a leak stops.

How can I fix/avoid this?