IT CRYSTALLIZES! It does not turn to sugar. Sugar is sucrose crystals, Crystals in honey are Dextrose sugars that are closely related to sucrose but the bees have converted it to an inverted sugar that the bees can use with out having to previously process it, like they do with sugar syrup or to sugar cakes placed on the hive.
Crystallization is somewhat dependent on temperature. Heat it to pasteurization and it will take the longest to form crystals when stored at any temp. freezing will slow crystallization to almost a stop put when moved and stored in a warmer temp the crystallization will speed up again.
Leave it on the hive, if it crystallizes so what, the bees can handle honey that has crystallized.