What we have found is this issue morphs depending on who is doing it and when. I found an email I made to Andy last summer showing it but I CANNOT recreate it now following the steps I detailed
We have seen the "one left behind" issue. I found laying more trench over it then deleting that trench *usually* gets rid of it but
not always and I have seen one point allow many hexes of trench to be laid but that was months ago and I cannot get the same thing now but I have managed to get trenches that show on the map as trenches but do not report as being trench
Andy is looking into it but it is looking like this might remain a weird little game quirk for all time but it DOES haves it's uses.... if you are on defence......which you would be if you are playing with trenches you can use them to clear lanes of fire by laying them then deleting them......which pioneers do with chainsaws and bulldozers in RL so ITS NOT A BUG......ITS A FEATURE
RE screenshots--------- set up an account with Imgur and you can post good-quality screenshots
https://imgur.com/
THANK YOU for putting in the effort to test this for us.