I have a different behaviour here:
My user can't just login again as you said, because the cache is not cleaned for user X even if user X logs in after the cache's expiration. I have to make user Y login, so that the cache is clear for Mr.X ... Wich is why I posted the question in the first place.
In theory, if I had only one user, then his cache would never be renewed ( if you follow me so far). Strange, no?