Why does the dragon on the portrait of King Lee Seong-gye of Joseon, now seen in costume, have five toes

In 1392, Yi Seong-gye made himself king, changed the country's name to Joseon, and set the capital at Seoul, which was at the end of the Yuan Dynasty. His father was the Yuan Dynasty's Daru Hua Chi (equivalent to a city secretary), and when he established the Joseon Kingdom, the Middle Kingdom was in chaos and no one paid any attention to him, so he made himself a 5-clawed dragon suit instead of a 4-clawed python suit