Man if stuff like seasonal flooding is actually already modelled and functional, then i am really impressed... Although, just as a precaution i would submit this to support so that devs can investigate it... Seems too drastic a change to be caused by seasons. Unless all the continents are pretty much one big plain (with some hills) and the water level during the flood is couple of meters.
EDIT: Hang on, was it classified as Water Worlds during your first visit? Cause i myself have discovered Water Worlds that, at the time, actually had continents and greenery, but were classified as WW anyway..
EDIT 2: And why is there no data for temperature and atmosphere?