Just encountered this bug today while I was attempting to finish up all the quests on Skellige. Unfortunately, I started the horse racing early on when I got to the island and didn't finish them all before I went and did just about every other quest in Skellige, so opening up a save file from that point would negate an enormous amount of progress.
Apparently this has been broken for over a month and hasn't been addressed in any patches, still broken in 1.06. I hope the devs finally notice us with this bug and fix it in the next patch. Pretty please?