In Season of Discovery the Ashenvale only mounts that are obtainable from friendly reputation get dismounted by fall damage and regular mounts do not.
Yeah it’s kinda annoying.
Also if you take damage by a mob you get instantly dismounted as well.
Normal mounts have a chance to get you dismounted, but currently this chance is 100% for the Ashenvale mounts which is a bug.
Its not a bug, these are not real mounts because they can only be used in one zone and don’t require training. It’s obvious that the instant dismounting is intentional to keep people from being able to flee as if they have a proper mount.