QDialog Extensions & resizing

[Bakuriu]

Hello,
I've got a problem concerning the way layouts resize their widgets when dealing with QDialogs and their extensions.
I already found a solution, but it seems to be deprecated; i'm talking about the setExtension/showExtension methods,but they have the problem that the extension I want to show isn't at the bottom of the QDialog but in the middle and anyway i hate to use deprecated methods.
I read the documentation and found out that the "new way" of showing extension is by using the show/hide functions on the single QWidgets.
But I tried to do some tests and this method seems to completely fail when resizing.I tried to use any method i knew for resizing the widgets and adjusting the size of the dialog but nothing seems to work.

I mean this:
Dialog when the extension is shown:




Note the size of the label...
and this is when i hide it:




As you can see the label changes his size.
What i wanted it to look like this:



Does anyone have a solution for this?
Thank you in advance.