To reproduce:
Put the command:
execute as @a[x_rotation=-90..-85,nbt={Inventory:[{id:"minecraft:elytra"}]}] at @s run tp @s ~ ~ ~ ~ -85execute as @a[x_rotation=-90..-85,nbt={Inventory:[{id:"minecraft:elytra"}]}] at @s run tp @s ~ ~ ~ ~ -85in a repeating command block.
Look directly up while flying with elytra. It takes some fiddling and a few tries to get this right. You may have to use firework rockets.
-> See that the arms and legs of your skin are gone.
Notes:
Your legs reappear whenever you are swimming.
If you take damage when you are without your legs or arms, they reappear, but will not play any animations.
If you die, the issue is fixed.
Seems as if this issue is fixed as of 18w16a. Please mark this issue as such!