one thing that never ceases to amuse me is the randomness of mine clearing.as shmavis commented,sometimes engineer squads will sit looking at a minefield with no other unit in close proximity and ignore it.other times an engineer squad,being micromanaged,with a complex movement order to reach a minefield will toss its last charge at another minefield it is passing when you have already detailed that minefields destruction to another squad.
i've even seen engineers that are cautious and crawling away from an arty ranging shot throw their charge and clear a mine.
with regard to the proximity of other units,i've only had a problem with casulties from the charge blast when the engineer squad has been ordered to target the minefield.