In this exemple, the size of the cell change when we resize the widget

#include <QtGui>

class TestButton : public QPushButton
{
protected:
void paintEvent(QPaintEvent *event)

{ QPainter painter(this); painter.fillRect(event->rect(), Qt::green); }

};

int main(int argc, char **argv)
{
QApplication app(argc, argv);

QTreeWidget *treeWidget = new QTreeWidget;
treeWidget->show();

qApp->processEvents(); //remove this line and the bug disapears

QTreeWidgetItem *topItem = new QTreeWidgetItem;
treeWidget->addTopLevelItem(topItem);

TestButton *testButton = new TestButton;
treeWidget->setItemWidget(topItem, 0, testButton);

return app.exec();
}