Look in source code \ Reflector.
There are lots of quirks in controls text processing, I doubt that any one will care to document this. For instance KeyDown event of TextBox is not fired when user presses BackSpace when there is text inside control, but fires when the is no text, etc. The quickest way to find how something work is to dig into source.
I have figured a nice rule: if for some reason you need to know how some control will behave is some situation don’t waste you time trying to code (reproduce) this situation, just get Reflector and look at source code.