Users with multiple groups

[tmscase]

I'm trying to set up a large amount of forums with multiple levels of permissions. Basically it should be something like this (one of many):

Learning Center Forum:
--Trading Materials
----Basic Trading
------Basic Trading Course
----Advanced Trading
----Shorting
----ForEx
--Training Videos
----Basic Trading
----Advanced Trading
----Shorting
----ForEx

Now all of our registered users have a primary group called "MWA Members" who have read access to Trading Materials, Basic Trading, Basic Trading Course, and Training Videos - Basic Trading.

I have set up groups such as "Shorting" and "ForEx" and "Advanced Trading" with read access to the appropriate forums. Now to my understanding, the way the permissions work with multiple groups is that a "Yes" always overrides a "No". Or a greater number overrides a smaller number. However if I give someone access to "Shorting" as a secondary group, it does nothing. If I then go and change their primary group from "MWA Members" to "Shorting", they then can see "Shorting" and not "Basic Trading".

Does anyone know what I might be doing wrong here? Or perhaps there's some sort of bug I don't know about? I've banged my head against this for a couple days now and need to find a solution....