Broken recurrences are not synchronized correctly with EAS and DAV

If you delete an event of a recurrence from the mobile at the next synchronization, the deleted event appears again.
The problem is present both using CalDAV and EAS

If you delete an event of a recurrence from the web interface on the mobile you will not delete the event only if you use CalDAV (with EAS being deleted)

Steps to reproduce:

• create a recurrence using the web interface
• synchronize the mobile device using both CalDAV and EAS
  case 1: delete a recurrence event from the mobile and force synchronization
  case 2: delete a recurrence event from the web interface

Expected behaviour:
case 1: the deleted event does not appear in the calendar
case 2: the deleted event does not appear in the calendar

Actual behaviour:
case 1: the deleted event appears again after synchronization with both CalDAV and EAS
case 2: the deleted event appears again after synchronization only using CalDAV (with EAS it remains deleted)