Designer: nested layouts take up space even when margins and spacing set to 0.

Using nested layouts in Designer, then even if setting all margins and spacing to 0, the inner layout will take up one pixel on each side so that a widget placed inside the inner layout will report a size smaller that it should have.

Can be reproduced in Designer by created a widget (200, 200).
Drag a QGridLayout onto the Form and set all margins and spacing to 0.
Add a QWidget inside this inner QGridLayout.
RightClick on the Form (the top level) and choose Lay Out in a Grid.

The inner widget should now have a size of 182, 182. (The top level size, take away the top level default margin)
Instead the inner widget has a size of 180, 180. The inner layout with 0 margin/spacing has consumed 1px on all sides.