Minecraft wiki entry for Texture_Update, associated text: The top texture of the observer is still largely based on the old "polished cobblestone" texture, rather than its updated version. This is apparently completely intentional.[8]
The top texture of the ender chest is still largely based on the old "cobblestone" texture, rather than its updated version. Mojang have decided not to fix this.[9]
The bedrock texture in natural end crystals has not been updated at all.[10]
The inventory and toast GUIs still use the old Knowledge Book texture, rather than its updated version.[11]
The Tutorial hints still uses the old oak planks texture, rather than its updated version.[12]
Spectator icons, such as the 'exit menu' and 'teleport to player' are still based on the old barrier[13] and eye of ender textures.[14]
The pack.png for the default resource pack still uses the old grass[verify] and cobblestone textures, rather than their updated version.[15]
The favicon for the game window uses the old crafting table texture, rather than the new one.[16]
Dyed versions of terracotta have not been updated, although their undyed version has.[17]
The Player Head still uses the old Steve texture in Minecraft Bedrock Edition despite the skin being updated in that version.