The grabImage() function from QtQuickTest will grab the wrong part of the screen if used on an item that is not a direct child of the main window.

If the source code available here is still the current one, then the issue comes from the way [x, y] coordinates of the items are used: According to the documentation, coordinates are always relative to the item parent, but in this function they are directly used as if they were screen coordinates, which leads to the incorrect behavior.