Must the copyright owner release GPLv3 derivative works?

[Mick Semb Wever]

--I'm new to this so forgive me if this is a silly question--


Given a company dual-licenses a product, for which it holds copyright to, 
under the GPLv3 and a commercial license, must they release all of their 
own derivative works under the GPLv3?

Also, if all derivative works based upon the GPLv3 offering must remain 
licensed under the GPLv3, can derivative works based upon the commercial 
license offering remain private?


For example is the following scenario possible:

The company's product contains modules A, B, and C.
C is a derivative work of B, and B is a derivative work of A.
The company holds copyright to all these modules.
A and B are available under the GPLv3.
A, B, and C, are available under the commercial license.

One of the company's customers having obtained all the modules under the 
commercial license writes a module D which is a derivative work of C.
This customer maintains copyright on module D.
And/Or this customer keeps the source code to module D private.

~mck

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