Hostile Mob spawn requirements broken.

according to minecraft wiki spawn mechanics you need at last 2 blocks of headroom above an opaque block to spawn a mob , the last two snapshots broke the spawn mechanic requirements for hostile mobs.

here's an example that tall mobs and spiders can somehow spawn on a piston with 1 airblock above. and get pushed on the glasblock.

if i close the gap between both quartzblocks, mobs can't spawn anymore.