Dimensions Misfunctioning

In my Lightbox settings Lightbox image display size is Original, and Image trigger size are choosen as Thumbnail and Preview. I use thumbnail size on teasers and preview on node page. For both of them, I would like to get Original size in lightbox when they are clicked. It works on teaser, when user clicks on thumbnail, lightbox appears and shows the pictures in Original size. But on node page, when user clicks on preview image, lightbox appears and shows image again in preview size... I want it in Original size again.

So... What can be done?