Iron bars are incorrectly mirror symmetric

The bug

The texture mapping for iron bars is incorrect, resulting in them appearing roughly mirror symmetric when viewed from the side, instead of roughly rotationally symmetric like the item texture.

How to reproduce

1. Place two solid blocks with a one block gap between them
2. Place iron bars in this gap

Expected results

The iron bars would look like the item.

Actual results

They appear Ш-shaped instead.