I had kind of a strange thought today. What are the odds that this false alarm guard problem has always existed but we didn't know about it until it became part of the user interface? As far as I know the filtering scheme hasn't actually changed. What's changed is that some alerts get through before a signal is fully processed. Makes sense, right? What else would they have done to it? So this could have been going on in the background without anybody even knowing it. Where the POP units are alerting and then cancelling the signal, a non-POP unit that works the same way would just stay silent. Or, if it's a range thing, it might alert for a while and then just stop when you came within closer range of the gun. That might be visual distance, it might not. In that case it would look just like instant on. These days it isn't all that out of place to see a trooper parked but not running radar.
I'm not trying to start a fire storm here, as I don't know everything. There might be other factors at work that only the VR engineers know about. But isn't this totally plausible? Especially considering that the effect that we're seeing is pretty rare to begin with?