I was doing some achievement hunting, so i grabbed a cosmaw and fed it a bunch, making sure it was tamed. Then, just to see if it worked properly, I jumped into the void with my elytra on. it kept bumping me but that's it, and then I got low I used a rocket, but it got in the way and I died to the void, making a corpse where I did.

I went back with the tried and true slow fall potion and chugging egaps, to retrieve my stuff, and the cosmaw didn't grab me no matter what I did.