I think the biggest unresolved bug has been to do with shields and saves for mounts; every file I can think of that has cavalry gives them a 6+ ward save with a shield and hand weapon. Also, Monstrous Beast and Monster mounts are inconsistently granting the proper +1 save bonus to mounted models. And don't think any chariots are granting +1Sv to characters mounted on them at all.
(All except for the O&G files
ofc. )