This is odd but might help. Since I began using ARC almost everytime I use another device other than the Vero 4k+ is my system (e.g Freeview or Sky+), when I turn the AVR and TV off the issue will occur and the Vero will some out of standby on it own.
On Wednesday I decide to try and get this logged, so I turn on loggin. The next half dozen or so time I used another device the Vero 4k+ did NOT come out of standby.
I wondered if it was have loggin on that some how accidentally blocked the problem. So on Thursady I turned off loggin, expecting the issue to occur. To my suprise after another half a dozen or so uses of the Vero and other devices the problem has still not occured.
I can only conclude that the reboot I did after turning on loggin has at least fixed the problem for now.
This might help developers find the root cause, but even not if you are having HDMI CE issues try a Vero reboot.