While you're previewing the form, you can check another aspect of the UI design. Note which line edit receives the focus when the form is open. There is a chance that the second line edit will be activated first. To check and modify the order of focus, close the preview and switch to the tab order editing mode by clicking on the icon called Edit Tab Order 
in the toolbar.
This mode associates a box with a number to each focusable widget. By clicking on the rectangle in the order you wish the widgets to gain focus, you can reorder values, thus re-ordering focus. Now make it so that the order is as shown here:
Our form only has ...
