Mirrored texture when inside a block

You do realize this was implemented to stop X-ray textures? You are looking at the back of a texture, it's supposed to be mirrored.

It's not the inside of a block, though. It's an overlay, and it's incorrectly-mirrored.

I do believe this is an intended effect. To give the player the feeling of seeing a block from the inside, although that's just speculation on my part. We'd need to see what a Mod or Mojangster says about it.

Steps to reproduce ?

Steps to reproduce are in one of the pictures but for copy and pasting purposes:
/setblock ~ ~1 ~ tnt
to reproduce (Works with some other blocks but I can only confirm tnt)

Good idea, TNT is a great testing block since it has text on the texture in vanilla, allowing you to easily see when it's mirrored or not.

Confirmed that the overlay, which is there on purpose, is mistakenly flipped backwards in 1.8.1-pre2.

IMO is that Working as Intended as the overlay should tell "Hey, you're inside a block and you're looking inside out."