(Minecraft) My horse, among other things, seems to have glitched out of existence. Help?

[CURIE]

I've recently gotten a PC version of Minecraft, and I've been experiencing quite a few problems lately. For one, my Compass and Map seem to randomly go into a glitched state where the Compass would point to some random point in the desert, rather than my spawn, and my map would just show me standing at the spawn, never moving. This would revert to normal whenever I quit and rebooted the game.

But then something more annoying happened. All of my achievements disappeared. No reason, I just quit the game one day, and when I came back they were all gone. I've since reclaimed all of them but one: the one for crafting a Notch Apple.

But the real problem, and the one I'm coming here to have sorted out, is the disappearance of my beloved horse. I haven't got a nametag to name her yet, but let's call her Midnight. Midnight is a plain black horse, wearing golden armor and (obviously) a saddle. I had her tied up in front of my house when I went underground for some mining, and when I came up she was gone. At first, I thought she had somehow been killed (despite the fact that she COULDN'T have, there's nothing around for her to kill herself with), and went off to get a replacement. When I came back with the new horse, to my (pleasant) surprise, she was there again, right where I left her, but with no lead.

I went to get a spare lead and tie her up again, but the lead was acting strange. You know how when you right click someone with a lead, it disappears from your hand and onto them? Well, that happened, but it went to the menu where you equip/unequip armor and saddles, AND I mounted her, all at the same time. AND, it never disappeared from my hand, as if it had cloned itself. I was like "okay whatever", dismounted, and tried to tie her to the fence, but it just wouldn't work. I tried the usual solution: save and quit (with Midnight standing RIGHT THERE in front of me), and when I came back, she was gone. Haven't seen her since.

Is there some way Midnight can be saved? A Minecraft authority or troubleshooting thread where I could post my save file, or something like that? And if so, what about my Notch apple achievement? I'd prefer to not have to spend all my gold on an award I've already earned.