Please note that we've updated the Mount & Blade II: Bannerlord save file system which requires you to take certain steps in order for your save files to be compatible with e1.7.1 and any later updates. You can find the instructions here.
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.