Often when I work in the designer it looses focus and I go back to the code editor.
Often when I click the wheel to move the screen. But also other things does it.
Also when I change font size it looses focus. Its very annoying.
And I would wish that the designer remember how it is set up every time you return.
Just click with the mouse fast on the wheel at the top left corner. The one that moves the view.
And if I add a label and click fast on the font size the problem occurs.