In Windows 7 fields behind grid did not have focus when click on datetime picker first.

I have a form as shown in the attachment...

When I open a form in windows 7, click on any date picker field on the form, and select a date.  After I selected a date; I cannot use the mouse to enter any fields behind the grid.  To get the focus; I click Show Grid button and select a row from the grid, and I am able to enter any fields behind the grid with a mouse.

It happened with Windows 7 not with Windows XP.  Does anyone get this problem, and advise how to fix this?  

Notes: In design I bring grid to front and send all fields to back.

Thanks,

Tony