TextBoxwatermarkExtender question/problem

[Dave]

I'm just getting started with AJAX using Visual Web Developer 2008
Express. I've started playing with the TextBoxwatermarkextender with a
bound text box. I've found that if I don't enter anything in the
TextBox that the Extender is assigned to, the WaterMark text is
inserted in to the record. Is that a characteristic of the WaterMark,
or should a Null Value get passed when I submit? Have I forgot
something?

Thanks