Locked chest texture is purple

This is because of the size change of normal chests. Locked chests are not meant to be used after the April Fools period, and so its texture has been removed as it is no longer used in-game. The pink color you see is one of the many unused tiles in terrain.png. I think this issue may count as invalid.

No this was not broken when chest size was changed, It worked Just fine Right up until Emerald Block was added. We all know that its not used but It is STILL IN THE GAME and server admins still make use of the ID for the reasons I stated above.

It worked after the chest size was changed because the texture was still the same size 16x16 for the smaller chest. The Locked chest model was still the full block size. Its not something hard to fix and I don't see how it can hurt only benefit.

Server admins use it because of its uncontainable state, not because it has a pretty texture. It's use as an admin tool is not gone just because it isn't textured properly. The locked chest takes up 6 tiles of textures, and confuses texture pack makers as to which is the real chest texture (only newbies, but still confusing). Mojang specifically removed the locked chest texture because it was unneeded, took up space and could be used for other textures (as shown by it being replaced by the emerald block.
In short, re-adding the textures would:
1. Waste space
2. Confuse new texture Pack creators
3. Not be any use - the locked chest lock can still be used as an admin tool, regardless whether it is textured or not.

This block is not supposed to be used in game. That it's supported at all would be the bug here 😉

The real issue is that there are very few blocks that cant be obtained and its confusing my users making them think their texture pack is broken when it shows up pink Can't it just use the same textures as the small chest? maybe even scale it down the same.. No doubt that would be even more work 😞

This could be used by map makers as a Fake chest to lure players into a Trap.

Fake chests could always be done with an empty normal chest instead. Placing locked chests that look exactly the same as normal chests would cause confusion as users would report an 'issue' where their chests in certain custom maps would not open - locked chests don't show any GUI anymore. Again, they can still be used by server admins regardless of their texture. I'm honestly surprised the block wasn't removed, especially since it takes up a block ID, which is currently limited to 255 and running out relatively quickly, with the new blocks like the beacon and anvil.

the reason why the locked chest doesn't have a "chest" texture is because notch needed more texture space for the block of emerald so he removed the locked chest texture and replaced it with a purple "missing texture" texture.

however when notch did add the emerald block the texture overlapped into the locked chest texture causing the emerald block texture to show as the top/bottom texture to the locked chest.

The block is not used in game, so they don't work for the texture of unused blocks.