I just verified this bug on a fresh install of SMF 2.0 RC4
No Mods
UTF8
3 users - Admin and 2 test users
What happens is that when Buddy/Ignore lists are disabled, all members are set to receive PMs from Admins only. However, I have verified that this restriction does not work. In the test forum, I have an Admin and two test users. They all have their PM options set to receive PMs from Admins only. However, both regular users can send and receive PMs from each other, and the Admin can receive PMs from both regular members.
The other problem aside from this is that if the users have their PM preference set to receive PMs from all members, and the Admin decides to change the main option to disable buddy/ignore lists, all members are changed to receive PMs from Admins only without their knowledge. The setting or disabling of the buddy/ignore lists function should not initiate a change in the user's setting of who to receive PMs from.
-sigh- There have been bugs relating to this since RC2 public when the buddy list/ignore feature was changed to what there is now...
Thanks for report!
I can confirm it, so I have tracked the bug in Mantis: http://dev.simplemachines.org/mantis/view.php?id=4596
Fixed with rev 10340.