QToolButton icon not updated in overflow menu

[pabakertx]

I have a QToolBar with several QToolButtons that change state (and icon) when clicked. This works just fine when the toolbar is visible. However, when the window is shrunk such that the toolbar becomes an "overflow" menu (accessible via the chevron icon >>), the icons do not get updated in the menu. E.g.,

if (state_ == Qt::Checked || state_ == Qt::PartiallyChecked) {
 state_ = Qt::Unchecked;
}
else {
 state_ = Qt::Checked;
}
QAction *a = defaultAction();
if (a) {
 a->setIcon(icon_[state_]);
}

if (state_ == Qt::Checked || state_ == Qt::PartiallyChecked) {
 state_ = Qt::Unchecked;
}
else {
 state_ = Qt::Checked;
}
QAction *a = defaultAction();
if (a) {
 a->setIcon(icon_[state_]);
}

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Note that the icon does get updated eventually, when the toolbar becomes visible again.

Is this a known bug in Qt4.2?