Layout.fillHeight is not working proper.

The attached Quick-application contains a Frame with a ColumnLayout as contentItem.
This layout contains Rectangle(blue) between a header and footer. The height of this rectangle grows with the window height using Layout.fillHeight: true. At the start, the application looks as expected. But when TextEditor gets focus and the X-button becomes visible, the blue rectangle shrinks and does not fill the left space of the window.
This snippet is working with Qt 5.15.* but not with Qt 6.
I get it working with Qt6, when I declare a invisible and empty Item in the ColumnLayout.