Pickers resetting

Pickers resetting

Hi,
I am very new to jQuery, but have managed to add a date picker and time picker to my form which works ok.
However i have a button to check the fields are all filled in before submitting the form. This button currently has no code, as i just added it.
However when i press it the 3 picker fields all reset to there initial state, which means i have to keep refilling them in, why would this be.
These are my 2 pieces of code, and the button as I say has no code attached to it, it is default button

<input type="text" id ="MyDate" />

$(function() {
                $('#MyDate').datepicker({ dateFormat: 'dd-mm-yy' })
            });