Yeah, UKHeliBob, it should be easy. I wrote a very simple bit of code as you suggested and the anomaly did not present itself.
So it would appear that there is something about my code, though the anomaly only appears on the two Every's , not the third one I have, nor on five other older Nanos, nor a Uno.
Not really worth pursuing at this point, I just thought that someone else might have seen something like it. Maybe it's just me.