Problem with default button and RequiredFieldValidator

[MatsL]

If I create a simple form with a panel a textbox and button and a
RequiredFieldValidator for the textbox. I define the default button on
the panel. When i open the form and press enter i get a warning from
the RequiredFieldValidator. If i press enter once more the page will be
postback even if the textbox is empty. If i click the button on the
panel with the mouse i get the RequiredFieldValidator error every time.
Any ideas why??

// Mats