dang horsies!
The other day I rode a horse back into the stable at a farm where I had helped so it wasn't stealing and the horse was standing weirdly on an almost vertical rock face... After that, the horse appeared wherever I fast travelled, as if it was mine. Even into Skyrim when I crossed the border.
Today that horse was nowhere to be found. So I figured it had returned to it's stable and went there to borrow it because uhm... I was over encumbered. I should probably get myself to that steed stone again... Anyway, the horse wasn't there so I borrowed its friend, went to the place where I dropped the loot, came back out and the dang horse was gone. Dropped the loot again and went to the stable outside of Bruma to buy a reliable horse. And there was the borrowed one, though it was already headed home. Again. The stable master said one horse was missing and they'd reward me handsomely if I found it so I figured maybe a free horse? Or at least a decent discount? So I found the horse, got ambushed by thieves, killed the thieves and had to steal the horse to return it.
Back at the stable I was rewarded 500 gold and the woman said she'd get the horse as soon as she could
(It was in her stable at this point - oh and the borrowed horse was there too. On its way home. Again.)
Well, I bought a horse and it was 3000 instead of the usual 1000 but OK, I'll just pick up ALL the loot (I was already over encumbered again...) and go back home to Skyrim to drop it off. I fast travel to Skyrim and then try to fast travel home but you can't do that when you're over encum.... hey! Where's the horse??? Apparently it stayed in Cyrodiil.
So I had to slowly walk to a nearby hiding place and get rid of all the extra weight so I can fast travel inside Skyrim and buy a second horse. Although I guess it's possible the horse will appear once I do fast travel. I should perhaps try that first.
And the expensive one better be waiting nicely on the other side of the border!