Fix a bug which could lead to incorrect state

synapse/state/__init__.py

@@ -769,6 +769,11 @@ def _make_state_cache_entry(
     delta_ids: Optional[StateMap[str]] = None
 
     for old_group, old_state in state_groups_ids.items():
+        if old_state.keys() - new_state.keys():
+            # Currently we don't support deltas that remove keys from the state
+            # map.
+            continue
+
         n_delta_ids = {k: v for k, v in new_state.items() if old_state.get(k) != v}
         if not delta_ids or len(n_delta_ids) < len(delta_ids):
             prev_group = old_group

synapse/storage/controllers/persist_events.py

@@ -934,6 +934,8 @@ async def _get_new_state_after_events(
             state_res_store=StateResolutionStore(self.main_store),
         )
 
+        full_state = await res.get_state(self._state_controller)
+
         state_resolutions_during_persistence.inc()
 
         # If the returned state matches the state group of one of the new
@@ -948,7 +950,7 @@ async def _get_new_state_after_events(
                 events_context,
             )
 
-        return res.state, None, new_latest_event_ids
+        return full_state, None, new_latest_event_ids
 
     async def _prune_extremities(
         self,