Is this a bug?

Today one of Pgpool-II users reported an interesting fatal error
message from PostgreSQL:

FATAL: terminating connection due to conflict with recovery
DETAIL: User was holding shared buffer pin for too long.
HINT: In a moment you should be able to reconnect to the database and repeat your command.

"User was holding shared buffer pin for too long" sounds unusual to
me. Is this a bug? PostgreSQL version is 10.1 according to the user.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp