This is very simple, but I couldn't find this reported as a bug already. Simply put, X-ray texture packs should not be a thing. Solid blocks should only be rendered as solid textures without transparency.  

This bug makes cheating way too easy and adversely affects servers. Sure, leaving options up to the player is always good, but this issue ruins gameplay and gives any cheaters a large advantage on servers.

The least that needs to be done is a server option to fix this. Then everyone will have the same experience and cheating will actually require cheating instead of just loading a texture pack.