Starcd has a bug? Buoyancy of water

Laure

Dear all, here is a very strange thing. I checked on a very simple design to be sure, here it is: || steel ||air going up|| steel || water ||

When the buoyancy of the water is not activated, then evrything is fine: the air warms up the steel which warms up the water. However, the simple fact to turn on the buoyancy for the water (not changing anything else) seems to stop the heat tranfer trough the wall, and the wall is not heated by the air, and so neither is the water!! Can someone explain that? It took me so many hours to figure it out, discovering that the programm was crap!!!! such a waste of time...unless there is a trick somewhere? Laure