A 2 stroke's porting is a compromise because, of necessity, it has to be symetrical around BDC so there's very little difference between the time the exhaust port opens and the time the transfer ports open, usually only around 10 degrees of rotation. This means there's still quite a bit of hot exhaust gas still in the cylinder when the cool fresh mixture begins to flow so there's a heat transfer between the two.

Contrast this with a 4 stroke which has assymetrical timing where the exhaust stroke is almost complete before the inlet opens.