DSM to many channels?

The documentation for the DSM2/DSMX protocols say "Note that many receivers with less than 8 channels require the Transmitter to send 7 or less channels."

Can someone please tell me what happens when you use to many channels on such a receiver? HH is telling me that I need to use 8 channels to control the GB200 on my 350QX, but doing so causes the quad to "chitter" as if the cyclic trim were non-zero.

I think that HH support is blowing smoke here, but want to verify that I'm seeing a known issue.

I can tell you that microbeast with dsmx sat receiver does not like 7 channels. I have to specify dsmx with 8 channels in deviation even though I only use 6 channels. I don't know if that restriction/limitation is part of the microbeast or the dsmx sat. Different receivers must have different expectations.