Wizard Frame should enable next automatically when previous is clicked
Right now it is the responsibility of the isNextEnabledInitially method for each wizard page to decide whether it should be enabled or not when loaded. This is fine, except if previous was pressed, next should always be enabled.
The logic in WizardFrame is in addCurrentPanel, which doesn't know whether next or previous was pressed. This can probably be fixed by modifying the previous button logic in WizardFrame to override the isEnabledInitially setting.