I suggest testing this in custom battle for those who can not accept it is a bug. I never use artillery in field battles or MP but I did run a custom test. The catapult I took would not move to new location after constant orders. It also did not fire. Finally, when I was beginning to wonder if CA had decided to make them static, I ordered it forward a tiny bit. At last it moved and I was also now able to target enemy units.

It is another bug! Similar to the grouped units that refuse to obey orders yet obey if ungrouped. In SP such things are an annoyance. In MP it is a game killer

.....Orda