Description:

Drupal post_install and post_upgrade changes owner of /var/lib/drupal which may be crucial, but I think if it shows a warning instead that would be more appropriate, so that user knows what's going on its system.

In some circumstances user may change /var/lib/drupal owner to another user due to their needs.

https://github.com/archlinux/svntogit-community/blob/packages/drupal/trunk/drupal.install:

post_install() {
chown -R http:http var/lib/drupal
}

post_upgrade() {
chown -R http:http var/lib/drupal
}