Delete stale checks and update cache

trans/models/unit.py

@@ -891,8 +891,10 @@ class Unit(models.Model):
 
             # Delete all checks if only message with this source is fuzzy
             if not same_source.exists():
-                self.checks().delete()
-                self.translation.invalidate_cache()
+                checks = self.checks()
+                if checks.exists():
+                    checks.delete()
+                    self.update_has_failing_check(True)
                 return
 
             # If there is no consistency checking, we can return