Most MP players will have the doctrine set for artillery to be the first priorty target for their artillery to fire at, if not, and you make Infantry or Cavalry the first priorty target, then you will lose all your cannons to enemy artillery fire....then your would be in serious trouble with no artillery. If there are no artillery to fire at, they will fire at the second priorty target, mine is set as Cav, and only after that, at any "threat" to the battery.
As I understand it, an Infantry advance (frontal) into heavy artillery fire will normally result in disaster, so the Corps is halting to attempt to silence the guns before advancing.
The doctrine may also be the reason, depending on how you have it set, a unit will not attack a superiour unit, if it "knows" it will be beaten - if you have it set that way.
I have played many MP games and don't regard what you have seen as a "problem".....note I'm saying saying your wrong and I'm right, but from my experience it has not been noted in the same way, and I don't re-call any other reports from others - yet !.