"Canceling authentication due to timeout" with idle transaction and reindex

Hello,

I am experiencing the following while using PostgreSQL
9.6.3-1.pgdg16.04+1 (deb package from official repository):

1. with "\set AUTOCOMMIT off" in my psqlrc, issue a
"SELECT * FROM pg_stat_activity;" and leave it there

2. in a different connection, issue a database REINDEX (of any database
different from 'postgres')

* Any further attempt to create new connections to the server, to any
database, does not succeed and leads to a "FATAL: canceling authentication
due to timeout" in the server logs.

* The REINDEX doesn't actually complete unless I end the transaction
started at point 1.

Is this expected? I am failing to see the relation between an idle
transaction in the 'postgres' database, a reindex operation and
subsequent logins.

Thank you very much for your attention,
Best regards

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