I noticed in Google Chrome that the edges of the crane figurine did not quite meet up, so that there were black lines in the body of the crane where the separate planes didn't quite meet.
I've noticed in the past that CSS seems to have real problems with this in other cases as well.
It's not constrained to CSS. Corners have always been a troublesome issue with 3D environments, and there are quite a few hacks needed to get it right. In many older games you used to be able to shoot "through" corners, as edge detection becomes difficult there. Minecraft still has issues with edges, and seeing what lies behind them is pretty common.
I've noticed in the past that CSS seems to have real problems with this in other cases as well.