Hi Jovirkku,
Thanks for replying. No, i didn’t synced after the OS update, because i only have local contacts. I make a backup for every update, and i flashed my phone during the last update (because of some problems). So the contacts come straight from the backup (with all the data included like birthdays)
Strange behaviour is that when i modify a contacts birthday-date to, let’s say 6 tot 7 december and then set it back to 6 and save, the birthday is shown in calendar and feed. But when I close the calender it immediatly removes the birthday from calendar.
I tried adding a new fake contact with a fake birthday and, voilá, its still there 
Is there an ‘easy’ solution or do I have to remove all the contacts and manually add each one of them to the people app?