Nether portals can generate on top of entities and suffocate them

I built a portal way out in the nether so I could access some new terrain to look for a camel, but the portal caused a chicken to suffocate when I travelled through it.

The portal in the nether was at -1500, 15, 1 and the seed is -5208210088792058538

The portal generated at -9998 68 11 in the overworld and apparently a chicken was there and it spawned on top of it.