Source Button - Cannot edit in Internet Explorer

It seems when using Internet Explorer only (tested on IE8), if you click the "Source" button. You are unable to edit or modify the code. You can select bits of code, or click your mouse to the area -- but then if you begin typing or using copy/paste commands they do not work.

Works fine in FF & Safari, I'm able to change and modify the code just fine. Doesn't work at all in IE8 though.