This is not a bug, simply an area where you need more intensive micro in order to use successfully. Once you learn how to handle cannons properly, things will go much smoother. Here are a few tips I use to micro my cannons, other people probably have others.
1) Let their army come to you, if possible. Use the 'stop' command to make your cannons unpack. Then they will be ready to fire as soon as something comes in range. For maximum effectiveness, target his cannons first, especially if he has culverins. The dirty secret about cannons is that culverins take 2 shots to kill a falc, and falcs take 2 shots to kill a culverin. The only difference between them is range. So if their culverins are walking towards you while your falcs are already set, you can get a volley of shots off and maybe even destroy their culverins before they get unpacked, if your enemy is dumb enough to let them wander into range (which happens frequently, as you've found out).
2) Don't target anything in the "Fog of War." The cannons tend to get confused, especially if you target something moving, then that target moves into the fog of war. Your cannon will stupidly move to the spot where their target was, looking for it. This is probably where you are losing most of your cannons. If you plan on opening a battle with cannon fire, try to put something ahead of your army with big LOS so that you can spot/maintain LOS on your targets.
3) If your target doesn't have the sword icon over it when you aquire it, don't right-click. Once in a while, the cannons have a hard time aquiring targets, and if you right-click then, the cannons just roll forward because they were told to move.
4) As much as possible, micro your multiple cannons to pick different targets for maximum effectiveness. If you can micro your 3 cannons to attack 3 different Lbows in a bunch, odds are good you'll manage to hit the whole bunch with at least one shot, while if you just click all your cannons to attack the middle, you'll only hit the Lbows in the middle. This is especially important when your opponent uses stagger formation, which they should.
Machiavelli_IUB