The only thing similar I have had happen, was the time when I had been drinking a seltzer water. I always bought the same kind, and it came in little plastic bottles. Sometimes I would take one to sip while reading in bed, and there would be some left if I fell asleep before finishing it. When I would get up the following day, if there was some left, it would understandably have gone flat, but I might still take a sip to see.
So one day I got up as usual and decided to take a sip from the half bottle of seltzer I'd left. When I sipped it, it tasted horribly bitter. I couldn't believe my eyes; because the entire bottle was filled with some kind of orange algae, as if it had been sitting there for a much longer time than overnight. I have never been able to explain this.