postfix contains a script to fixup various parts of the installation.
This script can set permissions on files.

However it also tries to fixup files installed by packages:
| chown: changing ownership of '/usr/lib/postfix/sbin': Read-only file system

Control: tag -1 + moreinfo

You described one aspect of postfix behavior, which is also documented
upstream.

What's the bug?  And what would be the expected behavior?

Thanks,

/mjt