Some 9.5beta2 backend processes not terminating properly?

After setting up 9.5beta2 on the Npgsql build server and running the Npgsql
test suite against I've noticed some weird behavior.

The tests run for a couple minutes, open and close some connection. With my
pre-9.5 backends, the moment the test runner exits I can see that all
backend processes exit immediately, and pg_activity_stat has no rows
(except the querying one). With 9.5beta2, however, some backend processes
continue to stay alive beyond the test runner, and pg_activity_stat
contains extra rows (state idle, waiting false). This situation persists
until I restart PostgreSQL.

This happens consistently on two machines, running Windows 7 and Windows
10. Both client and server are on the same machine and use TCP to
communicate. I can investigate further and try to produce a more isolated
repro but I thought I'd talk to you guys first.

Any thoughts or ideas on what might cause this? Any suggestions for
tracking this down?

Shay