Is that legal? You can claim ownership of derivatives??
IANAL, but I don't see why this would not hold up. It is their code, its in their license agreement (which is a contract you agree to). If you do not wish to give them the rights to your modifications, the license forbids you from using it
Note: by reading this notice you agree that all that is yours is mine, and all that is mine is mine also. ;-)
The license applies, wether you read it or not. The only difference is if you are aware that you are breaking it, or not.
Unless your use qualifies as fair use
(I know some jurisdictions have basic exceptions like "if you own software you can do what's needed to run it", but modifications?)