Snow and ice don't form properly.. There are these weird lines on the dirt/snow, you can see on the pictures. No matter how much time, they never get filled in.

Also ice doesn't form everywhere. you can cleary see on the "ice farm".. Some places simple don't turn to ice (all source block).  

BTW, it's a multiplayer server, i'm local host. 

EDIT: It's seems that doesn't snow in these places ..