I just ran some tests on this and there's a definite problem. I reported it as a bug.
The problem happens during initial deployment when you give an order to deploy on defensive line and the units immediately jump to their defensive positions. When this happens you might want to cancel the order (in the F7 Orders screen), detach the artillery from the corps, give the order again, place your artillery by hand, unlimber them, then reattach them to the corps (see below). Yeah, it's a bit of a pain, but it will eventually be fixed. If the units don't instantly jump to defensive positions, everything works normally.
Hook