Similar to the bridge-attacking bug with AI, the AI will also always attack any planted charges you place down if it blocks their path, literally killing themselves if you continue to plant charges down. It's kindof funny, but unrealistic, when they should technically ignore charges and only try to attack barricades, or bridges.
On the city-defend mission against the ebon riders, I placed a charge and barricades along the immediate north bridge, and the riders came to attack it, then blew up with the bridge, then swam to shore. I then created my own bridge with a charge at the other side. They attacked it again and blew up once more. And again once more. Only one rider remained at that point and I took mercy on him and left him in his confusion, since the bridge was gone.
Hm, good point. I've just put in an algorithm to make the AI at least partially take into account the damage characters are likely to take from killing enemies that have suicide attacks (which is essentially what explosive charges are, so far as the game is concerned).