pg_basebackup error: replication slot "pg_basebackup_2194" already exists

I ran into the issue described below with 10.0 beta. The error I got is:

pg_basebackup: could not create temporary replication slot
"pg_basebackup_2194": ERROR: replication slot "pg_basebackup_2194"
already exists

A race condition? Or maybe I am doing something wrong.

Release:
Name : postgresql10-server
Version : 10.0
Release : beta1PGDG.rhel7

Test Type:
Functional testing of a pacemaker resource agent
(https://github.com/ulodciv/pgha)

Test Detail:
During context/environement setup, pg_basebackup is invoked (in
parallel) from multiple virtual machines. The backups are then started
as asynchronously replicated hot standbies.

Platform:
Centos 7.3

Installation Method:
yum -y install
https://download.postgresql.org/pub/repos/yum/testing/10/redhat/rhel-7-x86_64/pgdg-redhat10-10-1.noarch.rpm
yum -y install postgresql10-server postgresql10-contrib

Platform Detail:

Test Procedure:

Have pg_basebackup run simultaneously on multiple hosts against
the same instance eg:

pg_basebackup -h test4 -p 5432 -D /var/lib/pgsql/10/data -U repl1 -Xs

Failure?

E deploylib.deployer_error.DeployerError:
postgres(at)test5: got exit status 1 for:
E pg_basebackup -h test4 -p 5432 -D
/var/lib/pgsql/10/data -U repl1 -Xs
E stderr: pg_basebackup: could not create temporary
replication slot "pg_basebackup_2194": ERROR: replication slot
"pg_basebackup_2194" already exists
E pg_basebackup: child process exited with error 1
E pg_basebackup: removing data directory "/var/lib/pgsql/10/data"

Test Results:

Comments:
This seems to be new with 10. I recently began testing the
pacemaker resource agent against PG 10. I never had (or noticed) this
failure with 9.6.1 and 9.6.2.

--
Ludovic