I've stripped my problem to this simple case.
The main window has a vertical layout. A text edit is in that layout. At run time the text edit should adjust it's size to the width and height of the window.
The text edit adjusts it's width according to the form, but it's height does not.
I've changed the layout to a grid layout and I've tried all kinds of size policies, but the height of the text edit does not change if I change at run time the height of the window.

What I really want is a window with a tab widget at the bottom that adjusts it's width to the form. But the height of the tab widget should stay 100px, independent of the size of the window.
Above the tab widget is a plain text edit that fills all the free space on the form. And of course the user must be able to adjust the size of the window.
Is it possible to do this in qt creator?