Discovery process addressing

[Milton Davis]

I have come across an interesting discovery behavior that the standard does not appear to address.
The DISCOVER_UNIQUE_BRANCH command is always supposed to be sent to the broadcast address: 0xff ff ff ff ff ff. However, what is supposed to happen if the DISCOVER_UNIQUE_BRANCH is sent to a specific UID as the destination address? This is obviously wrong on the part of the controller, but it is something that the RDM Integrity software does. It sends a discovery command addressed to the specific UID of the responder and it sets the parameter data (upper and lower bounds) for the same UID after it has narrowed things down to the single device. There are three possible routes to take in my mind:
1. Respond with a standard discovery response.
2. Do not respond.
3. Respond with a NACK format error response.
My products take route 2 as I have received an illegal command. I'm open to hearing thoughts from others on how this situation should be addressed.