Nether regenerates in smp after reconnect/server restart

I made a server for my friends to join. So it was all good until we made a portal to nether. After we entered it, i noticed some huge masses of errors in console. I though it's nothing big as far as server works great. Although i suppose nether didn't work very well if this happened... (below is more info)

What I expected to happen was...:
Nether world shouldn't regenerate every time server restarts or everyone disconnects

What actually happened was...:
Nether world doesn't save, which means, if you make something in nether, next time it will be gone

Steps to Reproduce:
Go to nether and modify it in any way (build/destroy something) and then:
1. Restart server
or
2. Reconnect (Make sure everyone else on server does it too)
Result: All your progress will be lost

EDIT Problem - Corrupted world data due to power loss