COM callbacks in cmldet

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I am writing cmdlet where I make a call to a COM component via
interop in a separate thread and I register a sink object to get
callbacks from this component . The worker thread is in a STA as the
call backs are generate when the call is in blocking state.
All is well and this works in other places.

But when have add this piece of code to a cmdlet the call backs no
longer arrive.
I am wondering whether there is any security settings which prevents
RPC threads from delivering callbacks to the shell

thanks

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