DeathTime values 20+ cause corrupted mobs

The bug

Basically, if you summon a mob with a DeathTime tag under 20, everything works fine. The mob will disappear as soon as it hits 20 (it increments every tick). Example command for this:

/summon zombie ~ ~1 ~ {Health:0,DeathTime:19}

But, if you summon a mob with a DeathTime tag of 20 or more, the mob goes through the entire death animation, but that's not all. The world thinks the mob is still there even if the client doesn't think so. So you can't place blocks where the mobs were and they seem to be unloaded or something. Relogging causes them to reappear and go through the death animation again, but still exist. I don't know how to actually get rid of these "corrupt" mobs. Example command to trigger this (beware that there's not any confirmed method to get these mobs out of your world, so make a new one just in case):

/summon zombie ~ ~1 ~ {Health:0,DeathTime:20}

Code analysis

Code analysis by Marcono1234 can be found in this comment.