Error creating Incident with Channel

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Today, I tried to add a Channel on to my Incident (and the new Threads) by adding a NamedID-style node for Channel to the Incident, but when I send the XML below I get an error "(soapenv:Sender) Data element in the Message is NULL".

If I take out the Channel node, the Incident is created and the Thread is added (although I don't get my channel obviously).

The documentation seems to say that adding a Channel on the Incident will add that channel to new Threads automatically ("Channel used in the creation of the most recent thread"). Is that incorrect and the issue is that I need to also supply the same Channel information inside the <object:ThreadList action="add"> node?