Confluence fails to non-conflicting merge changes while editing page concurrently

As per the documentation, Confluence should be able to merge non-conflicting changes successfully when two users are editing a page at the same time, but this doesn't seem to be happening.

Steps to reproduce:
1- User 1 opens page for editing, and enters text in one section:

2- User 2 opens page for editing, and enters text in another section:

3- User 1 saves changes, and gets the resulting page:

4- User 2 saves changes, and gets the resulting page:

The changes made by User 1 were lost, even though they were not conflicting. No errors are shown during the process.