Confusion regarding september long rating

before sept. challenge my rating was 1617 in long challenges and after the long challenge it got increased to 1709 but my overall rating decreased…is there anything about rating system that i don’t know or its a technical glitch!!

can someone help me!! thanks in advance…

Your rating might be increased due to participation in 3 hour contests. Your participation in long challenges is low. And your rating was less in long challenge but your overall rating was very high. So codechef expected you to perform according to your overall rating.