Hallo oracle3001,
thank you very much for that suggestion (PT4 Importer). It is one of the top candidates for the next update.
To deselect cards, you can use the right mouse button. You can also change this by unticking the option "Unselect Cards with Right Mouse Button" in the "Options" menu. However, this option only affects "Card Selection". Range Selection only works with the right mouse button so far, as most people have preferred this option.
Of course, you are absolutely right, this is not very clear. We might change this or make the "Right Mouse Button" clearer in the next update.
Thank you very much for your feedback and best regards,
Eisflamme