If the form that you are editing is being used at run time, you are warned that the form cannot be saved until no user is using the form. If you try to save the edited form, the save action is disallowed until the form is not being used.
When you access an existing form in the JADE Painter, you automatically lock the form class. Although locking a form prevents other users from making changes, they can view the unchanged form. When you exit from Painter, the lock is released.