What I expected to happen was...:
When I walked into my portal in my survival 15w31a-15w31c world for the first time, I expected to be able to explore the nether freely and log out in the nether with nothing wrong in the world.
What actually happened was...:
I walked through the portal and began to lag really bad where I could break blocks and they'd still be there (Which never happens on my computer. Game play is normally really smooth with no delay). I decided to log out in the nether then log back in, it seemed to work but I noticed an extra layer of netherrack over once exposed nether quartz. Once I came back to where my nether portal was supposed to be, it was no longer there with no evidence of it ever being there. I flew around in creative to check if I was lost but found no nether portal. My world seed is 21701249012995766975 in case you need it. I'm not sure if this is a bug or a byproduct from lagging but please look into it.
Steps to Reproduce:
1. Create a nether portal in 15w31c in a survival Minecraft world.
2. Lag horribly.
3. Log out in the nether then log back in right after.
4. Search for nether portal.
5. Accept your now stranded in the nether. 😞
P.S. I created a second world in creative and tried it out again but the portal was still there.
Cannot reproduce (in 15w32c)