Creating a page with a duplicated page title using the 'Create from Template' macro shows a misleading error

Summary

When trying to create a page using the "Create from Template" macro, if a page with a duplicated title already exists and the user has no permission to that existing page, the error message below appears:

The page fails to save.

Steps to Reproduce

1. Create a new template in a space called "Test".
2. Create a new page containing the "Create from Template" macro. In the settings for the macro, specify that the new page created will be based on the "Test" template created in Step #1.
3. Save the page.
4. Click on the "Create from Template" macro, which will open the page editor for you containing the "Test" template.
5. Name the page "Page A" and save it. The page will be saved successfully.
6. Restrict the page to just yourself for both viewing and editing.
7. Log out and log in as another user who has access to the previous space.
8. Click on the "Create from Template" macro, which will open the page editor for you containing the "Test" template.
9. Name the page "Page A" and try to save it.

Expected Results

You will be warned appropriately that another page with the title "Page A" already exists, such as the one below (seen in Confluence 5.9.12):

Actual Results

We see this error in the top right corner of the page instead: