Setting icon for Discard buton in QDialogButtonBox is not working

Setting stylesheet for QDialogButtonBox such as:

QDialogButtonBox
{
  dialogbuttonbox-buttons-have-icons: 1;
  dialog-save-icon: url(:/icons/save.png);
  dialog-discard-icon: url(:/icons/discard.png);
}

leads to changing icon for Save button but not for Discard button. Maybe it because of some inconsistency in qstylesheetstyle.cpp. There are "dialog-save-icon" and "dialog-discard-icon" items in knownStyleHints[] array but in propertyNameForStandardPixmap() function for Discard button "dialog-" part of string is missing:

case QStyle::SP_DialogSaveButton: return QLatin1String("dialog-save-icon");
...
case QStyle::SP_DialogDiscardButton: return QLatin1String("discard-icon");