I've had this problem develop a couple of times. Basically I have a conveyor dropping ice into my pool of water. When the ice amount is in the mg range, it doesn't melt until more ice is added to the pile.
The temperature of the ice is well above the melting point. Also attached is my game save file.
In a cold area, let water spill on the ground so that it freezes in micrograms. Move it to a hot area and try to melt it.