IMapControlEvents2.OnKeyDown not hit on Alt + key

Question

I want to catch the Alt key plus an addionally hit key in the MapControl's OnKeyDown. I did already set MapControl's KeyIntercept to esriKeyIntercept.esriKeyInterceptAlt but the event handler doesn't get raised on Alt or Alt + key. It does get hit on other keys. Any suggestions?

_mapControl.KeyIntercept = (int)(esriKeyIntercept.esriKeyInterceptAlt);

Handler:

void _mapControl_OnKeyDown(object sender, IMapControlEvents2_OnKeyDownEvent e)
{
  Trace.WriteLine("hit");
}