An IP lawyer was kind enough to take the time to share some knowledge with me. I was quite impressed with the way he boiled this down to something I could understand.

Here is a transcript:

Lawyer: Ok, first of all. The GPL is just a contract. It says if you do X (publish any modified code) I will not sue you. It is a contract between the licensor (Mambo coders) and you. UNLESS it has been assigned to someone else (like the FSF)

Lawyer: for example, Linus has assigned copyright in the kernel to the FSF, so if you violate the copyright on it, the FSF can sue you for infringement

Lawyer: So, in most projects the coders assign to a “project.” I don’t know if Mambo does this. If they do, then the copyright belong to the “project.” Otherwise each coder has rights in code he made

Lawyer: Therefore, if Mambo says in their FAQ that you can distribute your extensions under whatever license you want (and they own the copyright), then you are free to do so — they have modified their contract with you (the GPL)

Alex: ok, this makes sense

Lawyer: Second, the real big issue is the applicability of the GPL to extensions for interpreted languages.

Lawyer: The FSF is probably right about extensions to compiled languages … In copyright lingo you make a deritive work when you link (in the coding sense of the work, like ll) your extension with their
project …

Lawyer: For a “work” (in the copyright sense of the term) to be made it must be “fixed in a tangible medium.”

Alex: so if I don’t distribute it, I can’t “catch GPL”?

Lawyer: Basically, if you don’t distribute your extension on the same medium (like a cd) as a GPL’ed work you will definitely be fine (in my view).

Lawyer: Whats bad about this is that there is NO (0) caselaw on this issue

Lawyer: I can cite alot of analogous cases

Alex: wow, interesting… are there cases pending?

Lawyer: Nope.

Lawyer: Thats why the FSF GPL FAQ is so damaging. I know its wrong, other lawyers know its wrong (on this point), but there is no case on point.

Lawyer: Well, the last hope was the linksys incident

Lawyer: most cases are really straightforward wholesale copying of compiled code

Lawyer: Intrepreted code is a whole new game (in terms of law).

Lawyer: Its pretty intersting actually, I guess it has been less than a decade since intrepred code was a commercially viable option

Alex: Thanks, I really appreciate you taking the time to explain this to me.