We use rice-cooker in our daily life, but sometimes we get face some problem with it. The way they work is simply by temperature. When the water has run dry, the rice gets hotter and it senses that and cuts off. So it makes sense that when you add more water, it boils for longer/hotter to get rid of the water.
What you have to do is stop the machine before it's completely finished, and let it sit in the "keep warm" setting for the rest of the time until the water is absorbed rather than brutally boiled away by the machine.
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