Problem/Bug Can't modify

Hello Everybody,

So I made a mob farm on my server, but unfortunately I don't get many mobs, so I switched to a Craftbukkit server and now, my default monster spawn rate is 70. I changed it to 140, but whenever I start the server, it switches back to 50, for some reason. How can I fix that?
Can you help? 100001.dev 192168101.win routerlogin.win
Thank you