While playing on a friend's server, I was attacked by several monsters and killed by a zombie at the same time I teleported from overworld to the nether, when i respawned only a few blocks away, the items were gone in both overworld and nether.

Steps to reproduce:
1. join server
2. die while in portal 
3. repeat (I only got it to happen one more time after a lot more testing in a singleplayer world)

Most of the time the items would just appear in the other dimension, but apparently not always.