This bug allows a user to ride a mount as long as they feel like it without losing stamina.
What you need:
A mount
A shield / 1 handed weapon
All you need to do is tap parry once while riding your mount (Unsheathed one hander + parry) Your stamina will not drain while riding any more.
This is something that will be fixed fairly quickly I assume.
Yes, the stamina loss on a horse is minimal, but when you're being chased on horse by 7 alfars, every little bit count. lol
Edit:
Patch Notes:
- Mount running without stamina loss have been fixed