Editing a Page broken links are not shown in red

Summary

Customer reports that broken links to confluence pages are not shown in red color in a Page, while in Edit Mode, they are shown in blue instead.
On Read mode they are shown correctly.
The behavior is reproducible all the times, with any user.

Environment

Tested in several browsers (Firefox, Safari, Cloud), and several Confluence versions (6.6.5, 6.6.6, 6.10.0), same behavior
Tested 5.8.18, and it worked correctly: broken links were shown in red, in Edit Mode.

Collaborative Editing: On.

Steps to Reproduce

1. Create a new page in any given space, name it "Page 1", type any text, publish it.
2. Create another page, name it "Page 2", and in its text, add a link to the Page 1, publish it.
3. Delete the Page 1
4. Access the Page 2, notice that in Read Mode, it shows the link to Page 1 as broken (red color, underlined)
5. Click the Edit button
6. Notice that in Edit Mode, it shows the link to Page 1 as valid (blue)

Expected Results

Broken links to be shown in red color, even in Edit Mode

Actual Results

Broken links are shown in blue color in Edit Mode

Notes

It has worked as expected at some point, however, in newer versions that functionality was lost.
https://jira.atlassian.com/browse/CONFCLOUD-53848 shows it worked before.

Working in Confluence Server: 5.9.4

Workaround

Publish the affected page and the link will change to red.