step1: phenomenon

Create a QApplication and add  QFontComboBox, next press QFontComboBox Down arrow  until more than QApplication::doubleClickInterval() time,  and then release leftButton, the popup menu will hide. maybe this is not friendly to user.the phenomenon like newError.mp4

I tested on UOS1021, the phenomenon is same with Ubuntu19.04 and windows10. (tested Qt version is Qt5.14.2, Qt5.15.1, Qt5.15.2, Qt6.0.0 )

here is my test code:

#include <QApplication>
#include <QLineEdit>

// test code
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QFontComboBox b;
    b.show();

    return a.exec();
}

step2: Expectation phenomenon

hope QFontComboBox popup menu not  hide when mouse leftbutton press Down arrow, the press time more than QApplication::doubleClickInterval() value.