ICal doesn't save changes

I have a reoccurring (over several years) problem using ICal. If I change the number of times an event is repeated in the calendar, fx be repeating a job from 40 to 50 days, then the next time I open the calendar, the changes aren't saved. And no matter how many times I try to change and save, it keeps ignoring my changes. Has anybody experience this, and is there a fix?