Added key signature disappears after view change if its courtesy key is invisible
When changing from page view to continuous view and back, the key signature that had been changed during the piece and been made invisible is being deleted (jumping back to original key signature) hence destroying the most of the work. only an undo fixes the problem.
1. change key signature in the middle of the piece in a new staff.
2. make the courtesy key signature in the staff above (now in the end of the staff) invisible.
3. change to continuous view/
4. change back to page view
GIT commit: 3c7a69d