Display problem with ActiveQT component in Internet Explorer 10 and 11

[Annihilus]

Hi verybody,

I have to write an ActiveX component (with GUI) to be run in Internet Explorer.
As a test run, I have set up a new ActiveQT project with just one button in an otherwise empty window.
It works as intended in IE versions 8 and 9.
In 10 and 11, the UI is not being painted and the browser is reacting very sluggish, sometimes even freezing up completely.
When I then manually call show() or setVisible(true), the strangest thing happens:
The component is drawn, but outside the browser window as a completely new task.
When I close that, and then call show() or setVisible(true) a second time, the component shows up in IE as originally intended.
What's causing this very strange behaviour? Any help would be appreciated.

P.S.: Qt 4.8.4.0, Visual Studio 2010, Windows 7 and Windows 8

P.P.S.: I think the problem is related, maybe even identical, to the one described here:
http://stackoverflow.com/questions/21338198/a-qaxserver-example-does-not-display-in-ie