Does the GroupBox Header in WPF swallow mouse-clicks?

Question

Have a look at this very simple example WPF program:

Answer 1

It appears to be a subtle bug in the control template for the GroupBox. I found by editing the default template for the GroupBox and moving the Border named 'Header' to the last item in the control templates Grid element, the issue resolves itself.

The reason is that the one of the other Border elements with a TemplateBinding of BorderBrush was further down in the visual tree and was capturing the mouse click, that's why setting the BorderBrush to null allowed the CheckBox to correctly receive the mouse click.

Below is resulting style for the GroupBox. It is nearly identical to the default template for the control, except for the Border element named 'Header', which is now the last child of the Grid, rather than the second.