BUG #12828: False positive "parameter shared_buffers cannot be changed" error

The following bug has been logged on the website:

Bug reference: 12828
Logged by: Vincas Dargis
Email address: vindrg(at)gmail(dot)com
PostgreSQL version: 9.4.1
Operating system: Debian Wheezy amd64
Description:

To reproduce:

Install postgresql-9.4 from pgdg repository.

Check (default) shared buffers size:
su - postgres -c "psql -c 'show shared_buffers' postgres"
shared_buffers
----------------
128MB
(1 row)

Edit /etc/postgresql/9.4/main/postgresql.conf to add line at the end of
file:
include = 'custom.postgresql.conf'

Create file /etc/postgresql/9.4/main/custom.postgresql.conf with single
line:
shared_buffers = 256MB

Now, restart:

service postgresql restart

And check if shared_buffers have changed (yes it is):
su - postgres -c "psql -c 'show shared_buffers' postgres"
shared_buffers
----------------
256MB
(1 row)

But now, we ask to reload configuration without doing any more config
changes:

service postgresql reload

Then in file /var/log/postgresql/postgresql-9.4-main.log these lines
appears:

2015-03-04 21:39:27 EET [5290-2] LOG: received SIGHUP, reloading
configuration files
2015-03-04 21:39:27 EET [5290-3] LOG: parameter "shared_buffers" cannot be
changed without restarting the server
2015-03-04 21:39:27 EET [5290-4] LOG: configuration file
"/etc/postgresql/9.4/main/postgresql.conf" contains errors; unaffected
changes were applied

It warns that shared_buffers cannot be changed without restart, but there is
nothing to change, it's already 256MB as it where since the start of the
cluster!

So, "configuration file "X" contains errors" is a false positive.