Ok, so it seems the Mambo Foundation (or Miro, the company behind it) wants to take over control of the GPL'd content management system Mambo. The core developers have written an open letter to the community and want to fork the project. Slashdot reported.
Miro has now answered a few questions, see The Mambo Open Source Controversy - 20 Questions With Miro. Again, Slashdot reported.
Among the things the Mambo Foundation introduces are membership fees for 3rd party developers (US$ 1000 per year) and several penalties (even monetary) in the Terms & Conditions for developers who don't follow the rules.