Gap in sequence after fail-over

I have two test systems with Postgresql in Hot-standby configuration. The intention
is to fail-over to the slave every so often. When ever we switch servers (fail-over)
and start inserting data, the primary ids have a gap of ~30. From the following
thread form 2001 it seems this maybe expected?

http://archives.postgresql.org/pgsql-bugs/2001-12/msg00082.php

With a Hot-standby set-up like this, that regularly switches, can I not rely on
the sequence always incrementing by 1?

Thank you
Simon