Mobs not taking suffication damage by glass

the illager beast is not taking damge by being inside glass, when he should. the beast is not taking suffecation damage when it is stuck inside glass blocks and its hitbox is inside solid glass blocks

I did some more testing and it seems that this is the case for all the mobs in snapshot 18w43b. I did some more testing and found out that the bug exist in 1.13.2 aswell. Anyone know when it were first introuduced, or if it is a game feature?
I will test the rest of the mobs later, but I am already 99% sure that this is the case for every mob (exept vexes, since they do not take suffication damage)

i could not find this bug already reported, but if it is, please say it to me

How to reproduce: (use pictures as reffrence)
-go in to any world
-then make a 3*3*3 cube of glass, where you have a piston under so you can fill in the last glass block.
-place a mob under 2 blocks inside the room where the piston has taken a block away
-then activate the piston

for bigger mobs:
make a 4*4*4 cube of glass
destroy one block at the bottom
then place a mod in that space