Image size can only be increased to 900px

After inserting large images (1600px) via drag&drop into the editor they are displayed in original size (1600px) - as expected. But after changing the size from 1600px to 1200px the image is automatically scaled down to 900px.
Is it a bug or a feature?
If it is a feature then the scaling-down of images (to 900px) should be done when I (drag&)drop the image into the editor - and it should also not be possible to resize the image (to 1600px) by clicking "original".