When uploading images one after another, the images you've only just uploaded don't show up under the position (presumably because of MBS-4380).
That means that you can't set the position correctly because not all of the images are shown, and most noticeable for me, adding an image to the end doesn't mean it will be added to the end.

For example, on http://test.musicbrainz.org/release/f8799654-b84e-4cc5-bb64-636266267d07/cover-art I left each image as the last image in the list, so they should be displayed in the order I uploaded them. The order they're actually displayed in is 2 3 4 1 6 7 8 5.

What I assumed happened:

• Image 1 uploaded to position 1
• No images shown. Image 2 uploaded to position 1, shifting image 1 to position 2.
• 1 shown. 3 uploaded to position 2, shifting 1 to position 3.
• 1-2 shown. 4 uploaded to position 3, shifting 1 to position 4.
• Pause for a while, index updates.
• 1-4 shown. 5 uploaded to position 5.
• 1-4 shown. 6 uploaded to position 5, shifting 5 to position 6.
• 1-5 shown. 7 uploaded to position 6, shifting 5 to position 7.
• 1-6 shown. 8 uplaoded to position 7, shifting 5 to position 8.