If i am remember correctly. las time in school lab, I did an experiment regarding solubility on certain elements. Some element has better solubility in cool water. Dont know is Ca one of them.... One example. there is one powder that my mum use for cooking is more soluble when mix with cool water. Also some milk powder or protein powder need to mix with cool water first before add in hot water. From this observation, i think i believe what terryansimon said. Correct me if i am wrong