During thunderstorm, fire is made as cubes where lightning strikes. Rain does not extinguish fire if Game Rule "doFireTick" is set to false. This leads after one or two hours to a lot of fires in the map that can not be extinguished by rain and must be put out manualy by players.
Duplicate of MC-188, please use the search function to see if your bug has already been submitted. Currently over 54% of tickets are being closed as duplicate.