So I still can't submit bug reports (I just get a black screen), so I guess I'll report here that when two druids cast creeping cold on a single target it overwrites rather than stacks. This is really a huge problem, and means you can only have one druid in a raid group without drastically reducing their efficacy.
Luckily (I guess) druid is generally gimped enough that it's pretty rare to end up with two in a raid group.
Hopefully this is already known and being worked on, but I figured better safe than sorry.