My horse, and my brother's horse (both tamed, saddled, and armored) randomly disappeared in our singleplayer world after having the horses for two months. (We started the world when 1.7.2 was released, but this glitch happened currently in 1.7.4 obviously). Mine disappeared randomly when I was playing alone, I had left my horse in my stable, which is suffocation and escape-proof, it was a brick block building with a single-high fencepost row with gates blocking the entrance, and I have tested it, and there is no possibility for the horses to escape or die on their own in the building. I had only travelled a distance of maybe within 30 blocks away to my house, and when I came back only a few minutes later, the horse was gone, and neither his armor nor his saddle were on the ground either. He just vanished as if he never existed. And then my brother's horse disappeared after it had been tied up to a fencepost with a lead at a completely random interval. We were also still in the same chunk when this happened. Prior to this happening, we had also experienced a glitch where when we loaded up the world in LAN (this happened in both SP and LAN), both our leads were on the ground and our horses were untied. In fact, my brother's lead completely disappeared; I just got lucky that mine happened to still be on the ground. Once again, this was completely random and was caused by no external events or anything else in game. We are playing vanilla Minecraft and don't mod the game or do anything like that at all, etc.
Also, I am pretty sure that this is a glitch, and not a case of animal despawning, because I have travelled literally thousands of blocks away from my home and my animals literally dozens, probably hundreds of times, and I have never had anything, not even untamed animals or anything else, despawn at all! This bug has been reported before in a previous patch and marked as resolved; I do not think that it is resolved at all.