On the screenshot you can see what happens when I zone to another continent.
It also happens when I am getting a cutscene, like the ones used in the Harrison Jones quest chain in Uldum.
I can reproduce it 100% of the time.
Tested Kalimdor to Eastern Kingdom, Eastern Kingdom til Outlands and Kalimdor to Northrend.
If I use the portal to Mount Hyjal is does not happen, haven't completed any other Cataclysm areas, so those portals are untested.
http://peecee.dk/uploads/032011/fluidframes_after_zoning.jpg |