Hide and Show problem in master layout

[QPlace]

Fig.1 in the attached picture shows screen show of my dialog in Qt Designer.
When “Hide processor” button is clicked the hide/show of a top GroupBox processed as:

if (ui.gbGeneration->isVisible())
{
	ui.btnShowHide->setText("Show processor");
	ui.btnShowHide->setArrowType (Qt::ArrowType::DownArrow);
	ui. gbGeneration ->hide();
}
else
{
	ui.btnShowHide->setText("Hide processor");
	ui.btnShowHide->setArrowType (Qt::ArrowType::UpArrow);
	ui. gbGeneration ->show();
}

if (ui.gbGeneration->isVisible())
{
	ui.btnShowHide->setText("Show processor");
	ui.btnShowHide->setArrowType (Qt::ArrowType::DownArrow);
	ui. gbGeneration ->hide();
}
else
{
	ui.btnShowHide->setText("Hide processor");
	ui.btnShowHide->setArrowType (Qt::ArrowType::UpArrow);
	ui. gbGeneration ->show();
}

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Prior to clicking “Hide Processor” button the dialog capture in run-time is shown on Fig.2. After hiding the group box the result capture is shown on Fig.3

My question: how to change dialog layout in such a way that the result of “hiding” will look like as shown on Fig.4?

Oh, and one more thing – this dialog is shown in QMdiSubWindow when window is maximized.
Any help will be greatly appreciated, 3.5 hours had been lost already 