using setDate in DatePicker changes the page layout and adds white space at the bottom

using setDate in DatePicker changes the page layout and adds white space at the bottom

Hi All,
I'm encountering a problem with the setDate function in DatePicker UI.
I looked for a solution for 2 days without success. didn't see anyone else encountering this problem, except one unanswered post.

When I'm using the function, an addition of a block of white section comes to the bottom of the screen.
it happens only when I'm using the setDate function before the user actually chose a date in the datepicker.
if I'm using it after the user already chose, no white space appears.

this is the code I'm using.
(no special parameters are in the datepicker init)

var dateObj1 = new Date('2010/08/08');
$("#txttstate").datepicker( "setDate" , dateObj1 );

this drives me crazy... I'll be happy to get any advice.
(this happens in both IE and FF)
Thanks