I just made a new world in 1.2.3 and while I was exploring a cave, I found something that I though was an abandoned mineshaft. But it really didn't seem like one. Instead, it generated very strangely. Here is a picture:
Seed and coordinates are in the picture.
Seed and coordinates are in the picture.
This doesn't apply with all Mineshafts in 1.2.3 generated worlds, I just made one and found a normal Mineshaft.
Twitter: @EvanLange7737