I just tested this with swords and lances and with both weapons you can thrust straight through the horse. This will only bring back the old days of pump thrusting and I suggest that it'll get fixed asap.
dunno, i "think" that one of my spear thrusts went through the horse. could be however, that i had thrusted right in front of the horse, and as i moved the blade towards the horse again, the spear point was on the other side.