Fix some bugs

aleksis/apps/chronos/managers.py

@@ -878,7 +878,7 @@ class LessonEventQuerySet(PolymorphicQuerySet):
 
     def for_participant(self, person: Union[int, Person]) -> "LessonEventQuerySet":
         """Get all lesson events the person participates in (including amends)."""
-        amended = self.filter(Q(amended_by__isnull=False) | Q(groups__members=person)).values_list(
+        amended = self.filter(Q(amended_by__isnull=False) & Q(groups__members=person)).values_list(
             "amended_by__pk", flat=True
         )
         return self.filter(Q(groups__members=person) | Q(pk__in=amended)).distinct()