[mperham]

A license controls what OTHERS can do with your source. You, the copyright holder, can do anything you want.

[asymmetric]

Thanks, I stand corrected. How does this play with third-party contributions? Others might be the copyright-holders of a sub-section of the code.

[duckmysick]

Projects can have a Contributor License Agreement (CLA). It gives the owner of the project a right to republish (or copyright) the contributions. You can't contribute to the project without signing it.

[m4rtink]

This might also prevent a lot of people from contributing due to the added paperwork.

[JimDabell]

You ask contributors to sign a copyright assignment before accepting their changes.