The Calculating water table progress dialog is disappearing for the duration of the operation. It briefly appears but promptly vanishes. The 'calculating mipmaps' appears eventually and then the WT map. I've noticed that if you minimise L3DT and then maximise again, the missing dialog reappears on top and stays there as normal.
I checked all of the other maps and they are fine.
update
I think the clue might be that the terrain was all (way) above 0 alt but the water table was set at 0m in the dialog (ie default). When the WT is calculated it is blank as you would expect. Once I alter the WT alt to something in the region of 1000m it operates fine so I'm guessing that the min alt in that terrain is somewhere between 0 and 1000m.
monks