There is a possible bug with your character's stamina when sprinting with a mount. When sprinting with your horse, only your mount's stamina is supposed to decrease, but if you perform the following steps:
1. While unmounted, hold "shift" to sprint
2. Press "H" while still holding "shift"
Your character will mount and start sprinting with his horse. However, both your character's and your mount's stamina will decrease. The only way to stop it is to dismount and press "shift" again to stop sprinting.
Does anyone else encounter this? It's a minor but potentially annoying bug.
Patroller and Editor at
UESP