ZP-836 Completed occurrence of a recurring task duplicates in outlook.

Released under the Affero GNU General Public License (AGPL) version 3.

src/backend/kopano/mapiprovider.php

@@ -1727,6 +1727,11 @@ class MAPIProvider {
             // set recurrence start here because it's calculated differently for tasks and appointments
             $recur["start"] = $task->recurrence->start;
             $recur["regen"] = (isset($task->recurrence->regenerate) && $task->recurrence->regenerate) ? 1 : 0;
+            // OL regenerates recurring task itself, but setting deleteOccurrence is required so that PHP-MAPI doesn't regenerate
+            // completed occurrence of a task.
+            if ($recur["regen"] == 0) {
+                $recur["deleteOccurrence"] = 0;
+            }
             //Also add dates to $recur
             $recur["duedate"] = $task->duedate;
             $recur["complete"] = (isset($task->complete) && $task->complete) ? 1 : 0;