Regression: QComboBox popup listview expanding horizontal size policy does not work on 5.0.2

On Qt4.8 the listview popup from a QComboBox would by default automatically expand horizontally to contents.

On Qt5.0.2 it does not expand by default, and setting the view()>sizePolicy()>setHorizontalPolicy() to QSizePolicy::MinimumExpanding does not work either: The popup list view always has the view()->minimumWidth(), not expanding.

Also tried setting this on a reimplemented QComboBox showPopup(), which did not work either.