I want to try to make clear the problem I am seeing with the FORUM Module. All of this is in Forum release 04.04.03. I am trying so work with me here... if there are other questions I need to answer I am happy to do so. I am new to DNN and have only set up 3 sites using it. Be gentle with me. :p

It appears to be happening on this site as well as mine so I am confident there is a bug within the user/permission structure of the forum module.
HERE IS WHAT I AM SEEING.

If the admin settings are changed in any way, non-admin users set up prior to those admin edits are unable to post new threads.

All was working fine for everyone on my forums. I changed permissions to allow a group of users to administrate posts. (There is no moderation in the forums, but I wanted to restrict who could pin and/or lock threads.) I changed the forums to Public No Moderation w/Post Restrictions to activate the controls to remove permission for all registered users to pin and lock threads. I then applied those permissions to a new Security Role Group. As soon as I made that change the problem began where users could no longer add new threads.

ALSO, now I cannot seem to change any permissions on any forums in any group. The permissions simply revert back to what they were.

I attempted:

to make a new group and forum and the same problem exists in that new group and forum.

to go into the users and unauthorize and re-authorize a user and that had no affect.

creating a brand new user account. That user WAS ABLE to create new threads.

I have 2 sites up and running the exact same configuration.  Both are still in development and neither has data within it yet whic I am concerned at all about losing, so if I can be of any further help in setting up sceanrios, please let me know.