Logical decoding (contrib/test_decoding) walsender broken in 9.5 master?

It appears that logical decoding may be broken in 9.5 at the moment.

With HEAD at f6caf5a:

./configure --enable-debug --enable-cassert --prefix=/home/craig/pg/95 CFLAGS="-Og -ggdb -fno-omit-frame-pointer"

make clean install

make -C contrib/test_decoding clean install

PGPORT=5142 PATH=/home/craig/pg/95/bin:$PATH initdb -D ~/tmp/slottest95

PGPORT=5142 PATH=/home/craig/pg/95/bin:$PATH postgres -D ~/tmp/slottest95

and in another session:

psql -p 5142 -c 'SELECT pg_create_logical_replication_slot('test', 'test_decoding');'

in yet another:

PGPORT=5142 PATH=$HOME/pg/95/bin:$PATH pg_recvlogical -d postgres -S test --start -f -

and back in the psql session do some work:

psql -p 5142 -c 'CREATE TABLE x AS SELECT xx FROM generate_series(1,10000) xx;'

This works fine in REL9_4_STABLE at a44e54c.

Decoding over the SQL protocol works fine, and "make check" in contrib/test_decoding passes without errors. This issue only arises in decoding in a walsender.

I haven't bisected it back to a specific change yet, I just wanted to give early heads-up. Also, our testing clearly needs to cover logical decoding over walsenders.

See attachment for the bt.

--