MIDIFlushOutput does not cancel events scheduled over network

Calling MIDIFlushOutput on a network endpoint is not cancelling events scheduled with future timestamps -- they continue to send.

e.g.

func send(eventLists: [MIDIEventList]) {
    let outputPortRef = ...
    let networkDestination = ...

    for var eventList in eventLists {
        MIDISendEventList(outputPortRef, networkDestination.objectRef, &eventList)
    }
}

...

MIDIFlushOutput(networkDestination.objectRef)

I'm seeing that MIDIFlushOutput does successfully cancel scheduled events on a non-network endpoint. How can I clear all scheduled outgoing events over a MIDI Network connection?