grabKeyboard() affects ALL FORMS, even after containing control dies

Hello Folks,
I am sorry to bug you with yet another really complex issue. However, I have an app with two forms. The first one initializes as follows:
CGPIN::CGPIN(QString _message, QWidget *parent)
: QDialog(parent)
{
ui.setupUi(this);

...

ui.TxtPIN->setValidator( new QIntValidator(this) );
ui.TxtPIN->grabKeyboard(); //THIS LINE

showMaximized();
}

The form is then closed with close();, and another one is opened. In the other one, no keyboard events arrive to the keyPressedEvent handler even though the form, which grabbed the keyboard in the first place is long dead.

So the issue is this: once a grabKeyboard is issued, even if the control which grabbed the keyboard dies, the grab is maintained!

I will shortly upload a video explaining more.