Blog post titles for different dates within the same space must be unique if Collaborative Editing is enabled

Summary

If you enable Collaborative Editing in Confluence 6.x and create two blog posts with identical titles in the same space (whether they're created on the same day or not), Confluence throws an error message saying:

A page with the title 'blog 1' already exists in this space. Enter a different title for your page.

In short, this means the behaviour with Collaborative Editing turned on is as such:

1. Two blog posts with identical titles set for the same day cannot be saved.
2. Two blog posts with identical titles set for different days cannot be saved.

The behaviour is different with Collaborative Editing turned off / in Confluence 5.x, whereby the results are as such:

1. Two blog posts with identical titles set for the same day cannot be saved.
2. Two blog posts with identical titles set for different days can be saved.

This change is not mentioned anywhere in the Confluence 6.0 Release Notes.

Steps to reproduce

1. Install Confluence 6.0.4.
2. Create a space.
3. Create a new blog post for January 20, 2017 titled 'blog 1' and save it.
4. Create another blog post for January 3, 2017 titled 'blog 1' and save it.

Expected Results

The second blog post can be saved.

Actual Results

The second blog post can't be saved with the following error: