Featured image post/page – custom size

Hello guys,

I have a problem with my featured images for posts/pages. I’m using theme twentyfourteen. When I upload a picture, I want to change its size (crop it). It works, I save the image. Then I click on refresh in Set Featured Image window and I see that I cropped the image. So far so good. Now I click on save featured image, but oh-oh… The featured image in Edit page window is cropped, but differently; in other words, the featured image is just cropped original image, but that’s not what I wanted. Sooo, is it a bug or feature?

Does it mean, that I have to crop the image outside the wordpress first and then upload it to use it as a cropped featured image?

Anyway, the first picture that I uploaded and cropped as a featured image was cropped right and worked as intended, but I don’t know why. I only remember that at that time WP created only 3 extra pictures in the upload directory (so 4 pictures in total, while now it’s 9 or 10 pictures in total for each uploaded picture). I experienced this in last week, it happened on fresh setup of WP.