I just launched Minecraft after a month of absence, got on my horse and rode to one of my other bases that's far away. When I got there, I noticed that one of the five horses I keep there has iron armor and a saddle on it.

Now, I only ever use one horse, my main horse, because that's the fastest and can jump high. I chose that one because it was clearly better than the other five horses. I tamed all of these horses several months ago when I previous horse died. I keep all of the other five horses tied to fences at this one of my bases, without saddles or armor.

So, I definitely just received a free iron horse armor item (which I'm not complaining about), and a horse that has the same good attributes as my main horse (the amount of health is the same and the maximum jump height and riding speed seem to be the same, too [edit: I forgot to mention, they also have the same color and pattern]). However, this glitch concerns me because it could probably happen again with not-so-convenient results.

I'd also like to remind Mojang that MC-23320 is still unresolved and this glitch may be related to it.