Images become broken in edit mode when there is an automatic "Saved by merging changes"

Steps to reproduce

1. Enable Realtime WYSIWYG from Administration
2. Login with an user (e.g. U1)
3. Edit a page (I reproduced by editing in-place, if relevant)
4. Using another (incognito) window/tab, login with another user (e.g. U2)
5. Edit the same page by forcing the lock
6. Insert some images on the page with both users
7. Add/ edit some pieces of text and perform some saves
8. After an automatic "Saved by merging changes" success message is displayed on the bottom for one of the users, observe the images on the page

Expected results

The images are displayed properly in edit mode.

Actual results

The images become broken in edit mode, but they are displayed ok in view mode.

I couldn't successfully reproduce this issue locally it seems (I couldn't find a way to trigger an automatic "Saved by merging changes") using 2 users in 2 tabs, but it reproduced quite often while testing in real time with Gabi.

If I will find a way to reproduce this easier, I will update the steps.