I totally agree with Akka on this one. Charging with infantry makes only for the first two lines to actually engage the enemy, the rest just lug around in the background watching the spectacle and making some defensive stance. This might be what Akka refers to as units spacing out. I have found that I have to make a infanty-unit run behind the enemy target and order the attack when all the men on top of the enemy to actually have my infantry engage in melee properly. This happens both in sieges and regular field battles.

Regarding charging cavalry I almost don't bother anymore. Lately I have started to use cavalry to chase routers or melee other cavalry only, because of the issues with charges.

Another thing about the combat-system in this game: why even bother displaying the stats of units? For the most part the stats don't tell you anything how they will perform against each other. You only know this through trial and error. I engaged a unit of Armored Swordsmen head on with a unit of Pilgrims (this was on Med, no generals) and it managed to pin the swordsmen and perform extremely well, considering the stats.