I think there may be a bug with lance cavalry charging other cavalry - there does not seem to be the charge bonus you get when charging infantry. This is from another thread:

Quote Originally Posted by hrvojej
The charge of cavalry against another cavalry unit head-on has no effect, as far as I can tell (in 1 on 1 battles at least). Nobody dies until the secondary weapons are drawn.

I think that the lances are too short so when the mounts come head to head the lances don't reach the rider(s) - and nothing happens. Since they also have the same mass, they cannot push into each other's formation either. I am not sure whether this is intentional, but it sure doesn't look like the tales of medieval jousting matches.
May be saying nobody dies on impact is too strong, but there does not seem to be a benefit from charging.