Quick Custom Permissions question: How do I make a 'no new threads' group?

[Borgs8472]

Hey all.

An annoying poster has agreed to be allowed back on the condition that they don't make any new threads.

However I can't seem to get a usegroup to work correctly for them.

I made a 'no new posts' usergroup with 'can post new threads' set to 'no'.

I then made the poster's primary group this, however they can still make posts.

This is likely somehow due to the -3- secondary usergroups which they are members of, I have 2 for accessing hidden fora and one for having over 500 posts, all of which are allowed to make new posts.

If I turn their new thread permissions off, I've worried I'll mess things up.

So, if anyone with some decent knowledge of the permissions system could help me, that'd be great.