We don't need to detach. Since we're in the parent's destructor, it's already been done for us.

src/video_output/video_output.c

@@ -1223,7 +1223,6 @@ static void EndThread( vout_thread_t *p_vout )
     if( !p_vout->b_direct )
     {
         module_Unneed( p_vout->p_chroma, p_vout->p_chroma->p_module );
-        vlc_object_detach( p_vout->p_chroma );
         vlc_object_release( p_vout->p_chroma );
         p_vout->p_chroma = NULL;
     }

src/video_output/vout_subpictures.c

@@ -150,8 +150,6 @@ void spu_Destroy( spu_t *p_spu )
 {
     int i_index;
 
-    vlc_object_detach( p_spu );
-
     /* Destroy all remaining subpictures */
     for( i_index = 0; i_index < VOUT_MAX_SUBPICTURES; i_index++ )
     {