I don't think that's true. Eve can change the licence on her work. That doesn't affect any copy that Bob obtained beforehand. You cannot change the licence in a way that affects things already released - otherwise you'd be able to release something under BSD and after a year say "I'm changing the terms, new licence requires everyone to pay me X, even if you obtained the software on BSD terms".

Referring to the WTFPL author (http://sam.zoy.org/wtfpl/):

    Can’t you change the wording? It’s inappropriate / childish /
    not corporate-compliant.
    
    What the fuck is not clear in “DO WHAT THE FUCK YOU
    WANT TO”? If you do not like the license terms, just
    relicense the work under another license.

Yes, you can't normally do this --- as long as the license is valid. That's why you may need to defend it in court. (Eve may want the court to decide that the license never gave the right in the first place.)