1. Start the following example in QmlScene:

   import QtQuick 2.0
   import QtQuick.Controls 1.1
   
   Rectangle {
       width: 360
       height: 360
       ComboBox {
           model: ["test", "test2"]
       }
   }
   

2. Open the drop-down menu by clicking into the combo box.
3. ALT-Tab into another application.

The context menu stays at the top.
QmlScene does not get focus unless the user clicks inside the context menu.
It is not possible to close/cancel the context menu by clicking anywhere else.

This can be really awkward. See: QTCREATORBUG-11327