'thumbnail' edit doesn't work

[janmakinen]

When you upload some image, by the default 'thumbnail', 'medium' and 'large' sizes of this image are generated.
You can re-crop them by clicking on 'edit image' link.
If you check 'Thumbnail' on 'Apply changes to:', only 'thumbnail' size will be re-cropped (thats how I understand this feature).

But.
If you set 'Selection' in 'Image Crop' to actual 'thumbnail' size set in 'Media' page of the settings, nothing will be re-cropped and saved (first problem). Once you try, you lose the ability to check 'Apply changes to' option on the 'Edit image' screen, it disappears (second one).

How to reproduce.
Set 'thumbnail' in settings to '280x210'. Check crop option.
Upload some big image (bigger than 'thumbnail' size), click on 'Edit image' link in image edit screen.
Make a selection on image.
Find 'Image Crop' section. Don't fill 'Aspect ratio' (not tested), fill 'Selection' with '280' and '210'.
Set 'Thumbnail' in 'Apply changes to'.
Click on crop icon, and then on 'Save' button.
Get a response 'Image saved'.
You fill like you have re-cropped 'thumbnail' size of the image and new one was generated. It didn't.
Go to uploads folder, try to find your new thumbnail. There is still a previous one.
Something strange happened.

After this, inside '_wp_attachment_backup_sizes' of re-cropped attachment, we get 'thumbnail-orig' item. Its ok.
If you check '_wp_attachment_metadata', you won't find 'thumbnail' item anymore. Its disappeared. Like you don't have 'thumbnail' size set.
Thats strange. Logically, it should contain link to re-cropped thumbnail.

Tested on 3.3 and 3.3.1.

As of current trunk version, the bug can't be reproduced as janmakinen detailed. When you set the selection width and height to the same value as the thumbnail size, the crop button is disabled.