Consider this scenario:
- I am developing a program FooSuite that uses a GPL-licenced library QuuxTools
- I release the program FooSuite 1.0 under GPL
Later on I discover that, for some reason, I need to licence the program to someone on different terms.
I remove the dependency on GPL via QuuxTools, by either...
- rewriting the program not to use this library any longer
- obtaining a different licence for QuuxTools (if it's dual-licenced; see PyQt)
I release FooSuite 1.1 under a non-GPL licence.
However, FooSuite 1.1 is still a derivative work from FooSuite 1.0. I understand that it's not legal for a stranger to do what I did, but am I myself - as the owner of FooSuite - free from this restriction?