#1049 GCSM 4.3.0 Recreates Outlook Birthday Appointment from Google Birthdays Calendar

[John P Yelverton]

Related ticket: Support Request #969 — Duplicate Calendar Entries
GCSM version: 4.3.0
Outlook account: Outlook.com
Google Calendar account: Google account
Sync direction: Two-way appointment synchronization

Problem Description

I am experiencing recurring duplicate birthday appointments when using GO Contact Sync Mod (GCSM) 4.3.0 to synchronize my Outlook calendar with Google Calendar.

I understand that Outlook can create calendar appointments from birthdays stored in Outlook contacts. However, I believe my issue may be different because Google Calendar's contact-generated birthdays appear in its separate Birthdays calendar, while GCSM is configured to synchronize only the regular Google Calendar.

The GCSM log reports the following error:

Error saving existing Google appointment Joann Michelle Price's birthday - 2022-10-20 Recurrence. The service calendar has thrown an exception. HttpStatusCode is BadRequest. 'birthday' event type must not have private extended properties.

The log subsequently reports:

Updated appointment from Google to Outlook: "Joann Michelle Price's birthday - 2022-10-20 Recurrence".

Steps to Reproduce

Using Joann Michelle Price's birthday as a controlled test:

1. In Google Calendar, I confirmed that the green birthday event was in the Birthdays calendar and identified as coming from Google Contacts.
2. In Outlook, I found multiple blue birthday appointments in the regular Calendar, in addition to the green birthday entry.
3. I deleted the blue recurring birthday appointment series from Outlook, preserving the contact and the green birthday entry.
4. I deleted the corresponding blue recurring appointment series from Google Calendar, preserving the green contact-generated birthday event.
5. I ran GCSM manually with Sync Appointments enabled, Sync Contacts disabled, and automatic synchronization disabled.
6. After the sync, the blue birthday appointment reappeared in Outlook.
7. Google Calendar still displayed only the green contact-generated birthday event; the blue appointment was not visible in the regular Google Calendar.

Expected Behavior

GCSM should synchronize ordinary calendar appointments without creating a regular Outlook appointment from a Google Contacts birthday event in the separate Birthdays calendar.

At minimum, a special Google birthday event should not cause an invalid-property error or be recreated as an unwanted ordinary calendar appointment.

Actual Behavior

GCSM logs an error stating that a birthday event type must not have private extended properties, reports an update from Google to Outlook, and the deleted blue birthday appointment reappears in Outlook.

This occurs even though contact synchronization is disabled and the green Google Birthdays event is preserved.

Questions

1. Does GCSM 4.3.0 retrieve or process events from Google's special Birthdays calendar even when the configured target is the regular default calendar?
2. Could a stored synchronization identifier or match cause GCSM to recreate a deleted Outlook appointment from a Google birthday event?
3. Is this a known issue with Google Calendar API event types, particularly birthday events and private extended properties?
4. Is there a configuration option or recommended fix that prevents contact-generated birthdays from being synchronized as ordinary appointments?

I have disabled automatic synchronization while investigating, to prevent additional duplicates.

I can provide the relevant log excerpt and screenshots of the calendar settings and test results if helpful.
2026-10-16 11:47:32 | Warning | Error saving existing Google appointment Joann Michelle Price's birthday - 2022-10-20 Recurrence.
The service calendar has thrown an exception. HttpStatusCode is BadRequest. 'birthday' event type must not have private extended properties.
2026-10-16 11:47:32 | Information | Updated appointment from Google to Outlook: "Joann Michelle Price's birthday - 2022-10-20 Recurrence".

[John P Yelverton]

• Pertinent, most recent log file attached.

• The log records the event's title, recurrence, and Google event ID, but the excerpt doesn't establish which Google calendar ID was queried. So we still can't say conclusively whether GCSM is reading the special Birthdays calendar directly or encountering a birthday-type event through another route.

• the 11:47 run as the controlled test

  1. GCSM explicitly classified Joann's event as new
  At 11:47:05, the log says:
  No match found for Google appointment (Joann Michelle Price's birthday - 2022-10-20 Recurrence) => Add to Outlook
  That's direct evidence that GCSM decided to add the Google birthday appointment to Outlook.
  
  2. The Google event contains GCSM's private sync identifier
  At 10:29:48, the event's ExtendedProperties include a private property named gos:oid:Default_LWJPYX004. Google rejects GCSM's attempt to save that property because the event is of type birthday.
  This is an important clue: GCSM is trying to attach its synchronization metadata to an event that Google restricts.
  
  3. The log also shows that this isn't limited to Joann
  Gerald Keith Yelverton's birthday triggers the same API error. The log also shows other birthday and anniversary appointments being synchronized.