When I turn on the hot water in my kitchen it runs cold until I go into the washroom and turn on the hot water of my bathtub. Once that has run warm I turn it off and the water in the kitchen runs hot. I thought at first maybe it was just by the time I got back to the kitchen the water had heated up. So I played with the timing.
Nope. It's all about the bathtub.
It's kinda a weird thing.