The "all rights reserved" notice is redundant in any case, as copyright is granted implicitly and without restriction. It's completely optional. My point was that copyright itself is never waived in the first place. Instead, everyone is permitted by the rights holder to distribute and modify the work, provided they adhere to the stipulations of the license. A property owner can certainly give you permission to his property for any duration he pleases. But that doesn't mean you suddenly own his property, that he has lost any claims to it. Especially if this permission came with a contract forbidding you to do certain things. In the case of copyleft, this would be - among other things - to change or remove the original license, or refuse to provide the modified source code. Full disclosure - I'm not a lawyer. But I'm pretty sure this is accurate.