You may have found a bug. You should check the bug reports system to see if it's something known. If not, please consider opening a new report providing a minimal compilable example that shows that behavior.
I am not sure whether WiFi Direct is among the supported APIs which can be co-used for classic apps. But usually you need to take care of a couple of things.
Most promintently you will need to link against runtimeobject.lib to find Activation symbols.
I just pushed a change for positioning to showcase, how a "generic" porting from WinRT to classic apps can work. See https://codereview.qt-project.org/#/c/159330/ for some details.
I found the same problem with Marcosabba on Qt 5.5 for Winrt, too.
I have just tried to rebuild my application on Qt 5.6, today, it is fixed.
Drop down is shown below combobox control. But it still has a strange behaviour.
When item is dropping down, there is flicker frame.