press QComboBox long time, menu will hide when show with Popup mode

Hi,

create a QComboBox and add some items on linux platform(such as ubuntu, uos), press  QComboBox long time, the menu will show with popup window. and then release left mouse button(do not move mouse position), the popup window will hide right now.

analysis  file of qcombobox.cpp , the function showPopup of line 2577 , this code:

const bool usePopup = style->styleHint(QStyle::SH_ComboBox_Popup, &opt, this);

get the usePopup value always true on the linux, when i release left button, the eventFilter of line 744 will be run,

case QEvent::MouseButtonRelease will be  enter, there are two flag to control ignoreEvent value,   if   popupTimer.elapsed()  more than  QApplication::doubleClickInterval() , the ignoreEvent   will be false,  at this time, popupmenu will be hide.

the error.mp4  review the bug when  show  popup.    the right.mp4 is normal work.