[Owncloud] birthday in calendar-app

[stefan at du-weisst-schon-wo.de]

In my calendar app for all contacts i have a birthday date displayed. 
Thats cool, BUT not all my contacts have a birthday date given. That 
courses the calendar app to show me all my contacts with no birthday as 
if they have birthday today.

When i download the contacts as vcard, there is the line

BDAY:

And of course I find it in my Database oc_contacts_cards in field 
carddata as well.

I can delete it manually, and the contact disappear from calendar, but 
i have more than hundred contacts and I can image, I'm not the only one 
with this problem. And I dont know, if manual deleting this line can 
course data inconsistence in any way...

Any ideas?

And have I missed the possibility do hide contacts birthdays in 
calendar or isnt there just any?

Stefan