I have a Samsung Galaxy S3 with Android 4.1.2.
I have several calendars which I access through S Planner and it all work fine, except for "Contacts' birthdays and events". It shows the events and all, but if I change some birthday, or add a new contact with a birthday, the change doesn't show in the calendar.
On Google calendar, they are updated just fine.
I've found that if I clear the data of "Calendar Storage", it syncs again, and the events are shown properly. But then again, it doesn't update any new changes. Also, all the info not stored on Google Calendar, like tasks, gets deleted.