Drag & Drop still doesn't successfully create links if the actions are performed in the same time by users

Steps to reproduce

1. Enable Realtime WYSIWYG from Administration
2. Login with an user (e.g. U1)
3. Edit a page in-place
4. Using another (incognito) window/tab, login with another user (e.g. U2)
5. Edit the same page
6. Set the 2 windows to fit in the screen, but leave a spot for a 3rd window from which the Drag & Drop will be made
7. Select 2 larger files and drop the one after another for each user (I first dropped a file of 100 MB for U1 and immediately after that a 64 MB file for U2)
8. Observe the messages displayed
9. Save the pages and observe the links created

Expected results

There are displayed only messages for successful uploads for both users.

After save, both links are displayed on the page.

Actual results

After dropping the 100 MB file for U1, when dropped the 64 MB file for U2, a blue message was displayed for U1:

Upload aborted by the user.

After the save, only the link for the 64 MB file dropped by U2 was displayed (however, the files are displayed in Attachments tab).

Please see the attached .gif file.