Layout issue when a QLabel with wordWrap=true is inside a Stacked Widget

Create a groupBox with some QLineEdit.
Set a GridLayout for the groupBox and the Form.
When you resize the Form, the height of the QLineEdit is shrunk.

It works correctly if you replace the QStackedWidget by an other container (a
QFrame for instance).

The problem is visible from within Qt designer or at run-time after the .ui has
been compiled.

Reproducible from 4.5.2 to 4.6.1 at least.