If you change the title of a page, the change comment is not saved. The result is the same even if you change the page content.

To reproduce:

1. Create a new page, give it a title of "Title test", save it
2. Edit the page again, change the title, add a change comment of "title changed", save it
3. Edit the page again, change the title and the content, add a change comment of "title and content changed", save it
4. Edit the page again, change the content only, add a change comment of "content only changed"

Expected result: 4 versions of the page, 3 of which have change comments

Result: 4 versions of the page, 1 of which has a change comment

So changing the page title loses the change comment regardless of whether the content is changed or not.