Might be just me, but...

[Cypress Creek Test]

I'm pretty sure for the competitions that used to be "one horse per person", if you entered a horse and then sold it to someone else, you would be allowed to enter another horse (as you no longer owned the first horse).
Well, it's not letting me do that anymore, which is starting to become a real pain because there are some comps cough steeplechasing cough that I'd love to have run, but since they haven't since the last horse I comped and then sold... I'm stuck there. Idk if it's an intentional change or what but either way it's very frustrating lmao

[BlackOak2]

Not the way I remember it. You're still 'riding' the horse in that comp. Even if the comp hasn't run and the horse has been sold.
Maybe I remember it differently, though. I don't recall ever being able to enter a second horse in a competition where I already have a horse entered, because you'll still end up being the 'owner' of the horse in that competition once it does run. The new owner doesn't get that notation in the competition until they've entered the horse themself.

But maybe I'm wrong. Been wrong before!