QSplitter: When adding widgets to a splitter then they do not resize as expected if they were not explicitly parented to the splitter first

QSplitter: When adding widgets to a splitter then they do not resize as expected if they were not explicitly parented to the splitter first, even though one of the widgets is set to expand and stretch this is ignored and it stays fixed in place. The attached example shows this happening, if you parent the leftFrame and rightFrame to the splitter then it works fine.