[scorpio_rocks]

From patch notes for version 14:

Defending engineer infantry will now only clear mines, barbed wire and dragons teeth if they physically enter the hex containing them in order to allow defending engineers to sit just behind the defences without clearing their own defences. It has been a small anoyance for years that if you placed your own engineers just behind your defences they would start clearing them. They still can but when in the defence but now Enginners must enter a mined / Barbed wire/ dragons teeth hex to dismantle their own defences. In the defence they can no longer do that from one hex away.

I am pretty sure they only clear hex they are facing generally - this may need a test...