Running CentOS 6.5 users are being permitted write access to the cdrom/DVD burner due to an ACL. Users in the cdrom group should be the only ones permitted write access.
ls -l /dev/sr0
brw-rw----+ 1 root cdrom 11, 0 May 21 02:43 /dev/sr0

Booted in level 3, Pre-login sr0 permisions:
getfacl /dev/sr0
getfacl: Removing leading '/' from absolute path names
# file: dev/sr0
# owner: root
# group: cdrom
user::rw-
group::rw-
mask::rw-
other::---

Post login with idp account,:
getfacl /dev/sr0
getfacl: Removing leading '/' from absolute path names
# file: dev/sr0
# owner: root
# group: cdrom
user::rw-
user:idp:rw-
group::rw-
mask::rw-
other::---

The messagebus(DBus) seems to be setting this, but how and why? I say Dbus, because if the messagebus service is stopped the user specific permissions don't change when a user logs in.

You probably made your burner accessible to everybody when you set up your burner software so D-BUS is just doing what you told it to do.
Try to reinstall the burner software "single user only" for an authorized and non-authorized account and test it instead of a single installation using root-like authority (hence deriving "p_owner" rights from the installer) assuming you have an account that can install software but is blocked from the disk.

I think I have a solution better than the one originally suggested. Please, let me know if you see any holes in this approach.
1) Changed /usr/libexec/gvfsd-burn, /usr/bin/wodim, and /usr/bin/brasero to 750
2) Changed /usr/libexec/gvfsd-burn, /usr/bin/wodim, and /usr/bin/brasero to group dto
3) Created group dto
4) Added root and DTO users to dto group

Beware that patches may change these setting!

This does not change the fact that the DBUS daemon or some related service is dynamically applying an ACL giving all users write access to CD/DVD. It just prevents the users from accessing the tools used to burn disks.

If you add other tools like k3b for example, you will need to change the group and permissions on those as well.


PS.
This may sound like a simple solution, but it was not apparent what tool Nautilus was calling to do its burning (gvfsd-burn). And the dynamic ACL problem was a challenge I was reluctant to back away from.

I appreciate that and I found your efforts very informative, which is helpful for future issues.
Still, I'd do the install/re-install just to avoid having the problem pop back up later, we had a several sets of kernel patches in the last couple of changelogs so kernel maintenance seems to be our maintainers passion at the moment.