Shortcake appears to be causing images to be uploaded multiple times

[terrarum]

My company has been experiencing an issue with images are intermittently duplicated 3-30 times when uploaded. The images all have creation timestamps within the same 1-3 seconds.

I have been able to recreate this problem in a vanilla WordPress install with the following plugins enabled:

• Classic Editor
• Shortcake (Shortcode UI)
• Any plugin that uses Shortcake - tested with MaxButtons and TK SmugMug Slideshow Shortcode

Steps to reproduce

1. Go to a new article
2. Click Add Post Element
3. Close the Add Post Element box
4. Click Add Media
5. Upload an image
6. You get the error An error occurred in the upload. Please try again later.
7. Go to the Media Library and see more than one instance of the image

I was not able to recreate this with Classic Editor disabled. Switching to the new editor is not an option that my company has at the moment.

It looks like #814 could be relevant?