I'll lose all my downloaded books when I sign out which I kind of understand, but it is frustrating that I lose them too when the app thinks that I have signed out when I actually haven't! This happened to me time and again when there was ?a glitch going in and out of offline mode (mainly due to poor connection).
When a user is thought to be "signed out" the app, it is most likely one of the following is happening: (1) there was a problem connection, (2) it was an unintentional mistake made by the user, or (3) the user needed to do so (e.g. changing password), and in any of these three cases the user would sign right back in again, but he has lost all the the books that he has downloaded.
I wonder if it is possible not to remove the downloaded books immediately when a user is thought to have signed out, but rather removing them when the user successfully signs in to another account? This would avoid disaster in the above situations, while avoiding the scenario that a user gets more books than he is entitled to by signing in and out of different accounts - if that was the intention.
Of course I have no objections if I don't lose downloaded books at all at sign out, which seems to be how other apps are behaving. 