Invalid "Invalid Tag"

Rather a shock to hear from Lori Tribble, BTL Lab Manager, a few minutes ago that a number of devices fail the BTL-specified test 7.2.2.X2, "Non-documented Property Test" for property identifiers 255 and 256. It appears a number of new-to-BACnet developers are not conrsidering the tag extension rules in the last slide in my post BACnet tagging rules and when they reach a tag that requires two octets, they simply return "Invalid Tag."

I wonder how many devices that don't have the BTL Mark have similar shortcomings?

Update: Disappointing too to learn that devices are still failing MS/TP tests because of shortcuts in implementing state machines. I posted something related to this a couple of months ago: The machines are simple enough, just implement directly from the standard.