It is possible to upload multiple images in a media field where the cardinality is set to 1. When this happens you cannot save the node or remove 1 of the images in the field.
To replicate:
1. Enable media module (with media library).
2. Add a media field to the basic page content type.
- Set the limit to 1.
- Set the media type to "Image"
3. Create a new basic page.
- When filling in the media image field:
- first upload an image and insert it.
- remove this image (so you have an image in the library.)
- click 'add media' and select the uploaded image from the library
- when it is selected, upload a new image
- insert both images (when using the new Claro theme, you don't see that you have 2 images selected)
- now you can't save your page or remove any of the selected images.
Short video added where the issue can be seen