Maintenance for the week of November 25:
• [COMPLETE] Xbox: NA and EU megaservers for maintenance – November 27, 6:00AM EST (11:00 UTC) - 9:00AM EST (14:00 UTC)
• [COMPLETE] PlayStation®: NA and EU megaservers for maintenance – November 27, 6:00AM EST (11:00 UTC) - 9:00AM EST (14:00 UTC)
Ok, there's another side to this bug. If the passenger takes some action causing them to dismount while the mounting animation is playing, BOTH players dismount.
It even happens with such actions as the passenger opening the map right after using "Ride Mount".