There is a Russian tale why St. Nicholas has his feast twice in year:
Once upon a time St. Nicholas and St. John Casianus were wandering on Earth to help people, perform miracles etc. One day God called them to Himself, so they set off to Heaven. They were going through the forest when they saw a wagon stuck in mud and a peasant calling for help. St. John said that he won't appear in front of God in dirty vestments, but St. Nicholas didn't care and helped the poor man.
When they finally appeared in front of God (St. John - clean, St. Nicholas - in vestments covered with mud) God was shocked a bit and He asked what had happened. They told Him, and God was impressed by St. Nicholas' actions.
Since that moment St. Nicholas has his feast twice per year and St. John Casianus once per 4 years (of course his feast is transferred to 28th of February during non-leap years, but that is only a story