Hi there, no sure if this is a bug but the password reminder box won't show until the user has entered/changed their password initially.. IE all new users after activating the plugin will have their password stored. Those pre-existing won't be stored and therefore they would only be captured if they updated their profile for instance.
There is also the option to turn the system off in the settings... it might be off for you at the moment perhaps.
I have also recently moved the button to a user action so you only see the remind button when you hover over the users name in the back end.
Let me know if this helps or not.