Uploading images in editable long text properties fails

Steps to reproduce:

1. Create an AWM app with a long text and a content field
2. Create a new entry in the app and save it (empty)
3. Click the edit button of the long text property
4. Click the "image" button to insert an image
5. Go to the upload tab and upload an image and insert that image.
6. Save the property.
7. Repeat the edit steps with the content property, selecting a different image.

Expected result:

The image is displayed in both cases.

Actual result:

Only the image in the content field is displayed, the image that was inserted in the long text field is not displayed and also not listed in the attachments tab.

This is quite likely a regression introduced by the introduction of XWIKI-18810. To be tested on an earlier version.