Why some images are not allowed to be edited only for thumbnails?

Question

please see this:

As you can see, on the right columns I don't have the classic 'apply to' radios, where you can choose to apply modifications only to thumbnails.

It happens only with certain images, and I can't get the reason why. Apparently there are no diferent types or different contexts or conditions..

Any idea?

Answer 1

I've just found the reason why: the image is smaller than the thumbnail dimensions. That's the reason why.