textbox validating firing twice

[nidabp]

Hi,
I have a MDIParent form and 2 child forms. One of them,form1, has a textbox for which certain validations are present in the validating event. The other one has a button on it. When I try to navigate from form1 to form2, the validating event is firing twice for the first time. Is there a way to make it fire only once. And also, this event fires whenever I try to close the mdi parent form
Attached is a sample project.
Thank you.