Why does water evaporate from curry better when you off the gas then heat again?
Liquid in the pan actually does evaporate more quickly with boiling; however, you may be pulling more water out of your ingredients for a variety of reasons ie salt or acid is drawing off water. Or ingredients packed together in pan (mushrooms esp get watery packed together)

Surface drying of veg (not immersed )during storage may prevent further water loss when reheating.

Developing a 'skin' can prevent veg and meat from losing moisture.