Different areas, different spawn areas, randomNess and sample size. Change this big will never be right on first attempt, takes more data from various conditions to get right which is done by sampling many sources from the players. We did not get this overwhelmed in testing.
http://empireminecraft.com/threads/bug-attack-of-the-ghasts.14970/ Wasn't this of a bit of a high priority? The nether on SMP8 looks like about 20 nukes have gone off in it, especially North.
This is ridiculous, I've lost lots of stuff! I can't make blaze grinders for people, I can't travel in the nether without been blown up. I hope there is like a recovery fund for this, not just 500 rupees but closer to 10k! I've lost a lot because of this.