One of the more frustrating things, form submit that happens on enter key press anywhere in the web page. It was messing up some of my AJAX posts.
Solution, add a default button to the form (up the page chain to the initial master), add that button.
Like So:
<form id="form1" runat="server" defaultbutton="btnDefautNothing"/>
<asp:button id="btnDefautNothing" runat="server" visible="true" text="Nothing" style="display: none;" onclientclick="return false;" />
Should save some frustration.