Can not select qcombobox item with touch

Question

I develop Qt Application with a touchscreen. I use a combobox to display a list of computer comports. It works fine with mouse event, when I want to select an item from the combobox. When I use touch event, the combobox pops up the dropdown scroll, but I can not select an item from it with touch event.

For example, I can not change the selection from COM4 to COM6 with finger touch, but I can change it with mouse click.

How can I use finger touch to select item of combobox? Here is how I set the combobox items:

ui->bx_port->addItems(SerialConnect::GetSerialPortList());