Why behind some options for Project⇒Options there are 2 checkboxes?
The left checkbox behind some form element in the Project⇒Options specifies whether the value of the option overrides the same value of it from the parent mode (if checked – it overrides, if unchecked – the value of this option from the parent mode is used). So if the option itself has boolean value, then you see two checkboxes in one line.
