not all birthdays are shown in the calendar

[ReSqAr]

Not all birthdays are shown in the calendar, however there are on the phone as they are shown in birthdroid.

My setup:

• Android 4.4
• contacts coming from a Kolab account (This may contribute to the problem. I am not sure though. I have compared the Kolab files for one contact which is displayed and for one which isn't displayed and their structure is identical.)
• many contacts with umlauts
• I checked the free and the paid version on the Google store

I tried to extract log data via adb (as I have seen in the source code that a lot of interesting information is logged) but logging of the adapter seems to be disabled. Is there a runtime switch? I also tried to delete and restore all contact data multiple times. What I found interesting is that roughly the same contacts were not shown. I can help with debugging (but I don't have the Android SDK installed).