Taskbar close button does not work for floating windows

[mpondo]

When floating windows are set to display in the taskbar, the close button from the taskbar does not work. It appears to do nothing. However, it is also leaving the window in a broken state. If you then try to close window using the close button on the window itself, it closes the content but leaves an empty pane open.

Steps to reproduce in the TestApp:

• Configure the floating windows to show in the taskbar by adding <Setter Property="ShowInTaskbar" Value="True" /> to the style for the LayoutDocumentFloatingWindowControl
• Run the TestApp and float one of windows
• Go to the task bar and click the close button on the floating window

It appears that there is code specifically written to cancel the in the OnClosing event.