If you go to 'Edit Horse' from the 'Order Summary', add some changes to the horse and try to save, it gives 2 errors:
# To fill _all tabs_ (even though there aren't any as the Edit Horse is just a 1 tab page)
# 'Please check at least one discipline (there's a typo in the error message, to be fixed as well) checkbox' (because it's not showing the selected disciplines on Edit Horse page)

See the attached images for reference.