Vista - After IAudioClient::SetEvent the event is never set (Vista build 5

I'm trying to pass an Event handle to a capture device, in order to get me
signaled when a buffer has been captured. In the IAudioClient::Initialize
function I set the flag "AUDCLNT_STREAMFLAGS_EVENTCALLBACK" and I get a
result S_OK from it.
I played around with various durations too. The SetEvent function does
return with S_OK too. When I start the capture device it does start
capturing, however the event is never set. So this leaves my application with
cumbersome polling. Maybe the security system of Vista is preventing the
driver/service to set the created event. I played around with setting the
security by applying the most unsafe security descriptor but this did not
result in the event being set either. Is this feature working at all?

Martien