Well, this is a strange one.
After minimizing the game to system tray and restoring the game window, the AFK rider on the horse is still going. But the horse doesn't gain any EXP or lose Stamina. If the character gets off the horse, they'll be unable to get back on. Run away and come back, and the horse is missing.
But run back to where the horse was when sending the game to tray, and the horse is there. Can mount the horse and start riding again.
If the game isn't sent to tray, the horse behaves normally.
Anyone else able to verify the issue? I have to sleep so wasn't able to do much testing.
(I noticed there are more riderless horses than usual around heidel. )