It might be in your house.
In mine my little shite of a dear beloved 15 yo daughter thought it funny to swap the tops of the taps over to fool me and my best pal, who was visiting for a week, into thinking that a recent plumbing job had caused the hot water to the bathroom basin to come out of the cold tap and vice versa.
My best pal didn't notice (myopic, male, too chilled out to spot it, pick your reason!).
I however spent many hours on the net researching the cause and remedy to this peculiar phenomenon. I concluded that according to several Google searches the problem was a potentially very dangerous and hard to repair one. I even posted questions on here about it. Panic became my middle name.
I rang my landlord too....
... five minutes after which DD decided to 'come clean' :o and admit to her little trick.
I could have wrung her ruddy neck! :o