Example scenario using OwnCloud WebApp Contacts v1.5.5:
Contact maintained in Owncloud Contacts app (esp. birthday) -> Sync to Cloud -> birthday is displayed correctly in iOS -> customization of contact by emClient -> Sync to Cloud -> birthday is no longer displayed in iOS! -> Adjustment of the contact by iOS -> Sync to Cloud -> Birthday deleted.
Technical background: emClient converts the format:
In the OwnCloud WebApp “contacts” the date of birth is e.g.: 1983-08-29
After the example, the field then reads: 19830828T000000
Workaround: Do not write birthday in the “Birthday” field, but in the note field of the contact.
Of course this has the disadvantage: iOS does not report when someone has birthday…since it is not in the birthday field…
Can you reproduce the behaviour and is the error already known to the emClient team?