well entering a end portal there seems a 1 and 15 (estimate) minecraft seems to not convert your x y and z to the end spawn but teleport you to the end at you current over world x y and z causing a void death

example: end portal x y and z are -185 28 -595 end spawn is at 100 49 0

now sometimes wane entering instead of spawning at 100 49 0 you will spawn -185 28 -595 causing death and lost items