I was playing the new Minecraft 1.13 beta with a new custom skin, and I noticed a painting behind me glitching out, it looked like some fragments would turn invisible from different points of view.

The glitch applied for the image layer, and the actual painting frame layer.

Next thing I've noticed: some mobs have the same issue, the "panels", I guess you could call them, that make up the shape of the arm are having the same weird texture glitch.

Final thing, anything I hold seems to protrude from just above my elbow instead of appearing in my hand.