Include.d and warnings

We've set up an include directory in postgresql.conf:

include_dir = 'conf.d'

The include directory has a file that changes the value of
"max_connections".

Now when we reload Postgres, an error appears in the logs:

-----
parameter ""max_connections"" cannot be changed without restarting the
server
...
configuration file ""/var/lib/pgsql/9.4/data/postgresql.conf"" contains
errors; unaffected changes were applied
-----

But max_connections did not change before the reload. It is just
overruled in an included configuration file.

Is this behavior "by design", or should Postgres not give an error under
the above circumstances?

Kind Regards,
Andomar