Happened to my friend's Vios once in Cameron Highlands. It had been parked overnight outside the hotel and after a short drive in the morning, the key could not be pulled out when he wanted to park the car. He went to a workshop there and the mechanic sprayed some WD40 into the keyhole and voila, the key could then be taken out after some gentle wriggling. That was the one and only time it had happened. My friend believes whatever the root cause of the problem might be, it would never happen at normal temperature in the city.