Since the fixes MC-89760 and MC-82464 the compatibility with old non-transparent skin are broken.

See the jomo 's image from skin pattern (see above linked image):
The top right pink transparency detection square exist for compatibility reason (with non-transparent skin, like Notch skin, and only with 64x32 pixels skins). All others detections square can be remove.
See MC-89760 for more explanation about this bug.

Possibles solutions:

• Apply the transparency detection only on 64x32 pixels skins
• Apply the transparency detection only on the top-right 32x32 detection zone
• Revert the MC-89760/MC-82464 fix

The MC-89760 and MC-82464 fixes create more problems and impact more users than the original reported bug.