Multiworld and biomes problem

When 1.5 came out I set up a server with the official server software. We built a town on a big snow biome.
Today I decided to update my bukkit server running #670 to #714, my plan was to incorporate our new world to our existing bukkit server using the multi-world features. It was my first time experimenting with multiple world so I installed the plugins MultiVerse and MultiInv. The original world was called 'world' and the new one 'esno'.
After I set it up I noticed that the biomes of the 'esno' map had changed. Just to check if it was a problem with the world files or the server I set up another #714 server without plugins or anything and moved the 'esno' world there. Nope, it wasn't a problem with the world files, the biomes were correct.
I went back to the multi-world server and decided to switch the world folders, I moved 'world' to 'esno' and viceversa. This time esno's biomes were correct, but the original world's weren't. This time I also noticed that somehow all the worlds 'inherited' the biomes of the default world, that is, when 'world' was the default, 'esno' copied its biomes, and viceversa.

I wonder if this the expected behavior or a bug in craftbukkit or any of the plugins I had. I spent a long time searching this forum and the internet, but I didn't find anything (perhaps I was using the wrong keywords?)
Anyways, here are the specs of the server:
Linux 2.6.35-28-server #50-Ubuntu SMP Fri Mar 18 18:59:25 UTC 2011 x86_64 GNU/Linux
java version "1.6.0_24"
Java(TM) SE Runtime Environment (build 1.6.0_24-b07)
Java HotSpot(TM) 64-Bit Server VM (build 19.1-b02, mixed mode)

I'm running Craftbukkit #714. I have a bunch of plugins, but during this test I only used MultiVerse, Permissions and WeatherMan (so I could easily see the biome changes)

If it is of any help, the 'world' map was started around December, a couple of weeks before Beta (I don't remember the exact Minecraft version), whereas 'esno' was generated the day 1.5 came out.

I'd greatly appreciate any help on this issue.