There are some serious issues with the event calendar. There are a lot of variables used which are never initialized. There are also a lot of other variables in particular the post variables which are never properly checked. There are a lot of redundant variables used in two different places for the same thing. There are also variables that are set on one place and reinitialized to another value when a local variable should be declared and used. This application is very unstable and buggy. I causes periodic changes to random months or month that are several years in the past. I have reworked the problem code to put in proper checks. Someone need to look over the app for these issues.