MahApps/MahApps.Metro — pull request #1291 by Dotnetifier (2014-04-11 17:27:31+00:00)
Title: Click on Expander header support

I noticed that the Expander control does not open when you click the header text, which is not the default behavior, and may be annoying.

I set the Header as the content of the ToggleButton that determines whether the Expander is open or not, which fixed the problem.