4.4.1 post-thumbnail/featured image not updating

Since the 4.4.1 update, new media library image uploads create post-thumbnails/featured images that do not match my settings/media/thumbnail size. These settings have not changed since 4.4: 250, 250, crop thumbnail to exact dimensions. The thumbnails are not square as they should be.

When I try to correct this by editing an image in the media library, cropping the image to be square, and choosing to apply this change to the thumbnail ONLY. It looks like my thumbnail/featured image has been updated. But when I add this image to a post, the proportional version of the full-size image is set instead of the square I just created.

I am using a twenty-fifteen child theme.

How can I get my squares?

[ No bumping please. ]