Why does overriding the WPF [removed] method fail to draw to the screen?

Question

I noticed that when overriding the System.Windows.Window OnRender method fails to draw to the screen. I\'m sure there\'s a good reason for this but was unable to find the explan

Answer 1

The answer is given by Chales Petzold here.

His answer is 'don't know why', however a comment correctly suggests that setting the window's Background to transparent fixes the bug.