-Ice glitch:
Freeze the aliens their create a different hitbox (at least that's how I perceive it as a player), what makes clipped marines and aliens with each other, this creates teleportation or makes the marines fly on the backs of the aliens.
Dead frozen aliens are a completely different entity type (to make the shattering animation work), but I'm pretty sure alive frozen aliens don't change their collision hull. This is probably more complicated than originally thought. A demo might help here.
For Ice glich this doesn't only happen on dead aliens.
Imported from https://steamcommunity.com/app/563560/discussions/2/6670425060425619954/:
Dead frozen aliens are a completely different entity type (to make the shattering animation work), but I'm pretty sure alive frozen aliens don't change their collision hull. This is probably more complicated than originally thought. A demo might help here.