Steps to Reproduce:
1. tame a parrot
2. have it try to land on your shoulder
3. while it is still pathing to you, walk into a nether portal
4. this seems to only work after 1 failed try, so repeat the process from #2 until the crash occurs

Observed Results:
Game crashes and world / realm rolls back (notice the obsidian placement before and after the crash in the attached video).

Expected Results:
Game doesn't crash and you go through dimensions fine

Related Issues:
1. MCPE-51386
2. MCPE-27950

Within the past 4 months, our realm has crashed/rolled back many times due to members not being aware that they should keep parrots away from portals. We try to keep this info secret from them to avoid chaos, but a few are starting to figure it out. This issue has been reported before, but I don't believe it was noticed, so I'm submitting a new issue along with a video demonstrating it.