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It is real. The evidence is an easily repeatable experiment.
The reason for it is that when water is hot, it is more likely to evaporate. This removes heat from the system and leaves the remaining water colder. It also means there is less water remaining to freeze, requiring less overall heat loss, even if its temperature is higher.
Also, note that due to the latent heat of fusion, a gram of water has to lose twice as much heat going from liquid to solid as it does going from 40 C to 0 C. The initial temperature is not as important as you might think when it comes to the total amount of heat that must be lost for water to freeze.
In a sealed container, one that is poorly insulated, and in high humidity, the effect is not present.