Subject pretty well explains it. We upgraded form 3.5.1 to 3.6.3 and now anytime I put PLAIN in the config it is replaced with
My openfire.xml behaves this very same way, yet I’m still able to authenticate, either SSO (GSSAPI) or PLAIN. I believe it’s because this parameter has been migrated to the database instead of having to be set in openfire.xml exclusively. Someone else may be able to clarify why this acts the way it does, but I’m just chiming in to let you know that you’re not crazy.
Most settings are now migrated to the database. If you enter a setting and restart openfire the changes are moved into the database. You can now change most settings via the system properties on the admin web site.