Extra space between page title and content when content header region is empty

Problem/Motivation

I am not sure what causes this, but on admin pages with an empty content-header region, there is an extra gap between the title and the main content.

I can't figure out what's causing it though. The empty region has some margin on it, but removing it doesn't do anything.

Screenshots showing the end of the page title and start of the content, with a large gap in between.

Steps to reproduce

1. Install Drupal from head
2. View any page with an empty content-header region, e.g. the Status report page
3. See there is a large gap between the page title and contents
4. View a page with content in the region, e.g. the Content page
5. See the spacing looks correct

Good spacing

Bad spacing

Proposed resolution

Figure out what is creating the gap and remove it :)

Remaining tasks

User interface changes

Introduced terminology

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

N/A