What would cold come out of hot and then stop

Depending on faucet style cold can come out both sides . if no water filling up other side or water in hot lines it works like a mixing valve.

It takes cold water and mixes it with hot water so it won’t get to hot. Have to have them in school systems so kids won’t scald their hands . Water heaters must be set on 140 degrees in Ky per health department. But at those temps little kids will burn .