UI layout error in Form Editor when dragging item from one positioner to another

In Form Editor :

    Create a row positioner containing two checkboxs

    Create a column positioner containing one checkbox and one button

Then in Navigator :

    Drag the button from the column positioner to the row positioner

The position of button is not shown in the right place. ( error.png ) I have to click "Reset View" button in Form Editor to get expected view. ( expected.png )