Many elements use something like:
overlay->video_sinkpad =
     gst_pad_new_from_template (gst_static_pad_template_get
     (&video_sink_template_factory), "video_sink");
in their _init function. This is wrong since gst_pad_new_from_template creates a copy of its parameter:

static void
gst_pad_set_property (GObject * object, guint prop_id,
    const GValue * value, GParamSpec * pspec)
{
[...]    
   case PAD_PROP_TEMPLATE:
      gst_pad_set_pad_template (GST_PAD_CAST (object),
          (GstPadTemplate *) g_value_dup_gst_object (value));
      break;
}


GstPad *
gst_pad_new_from_template (GstPadTemplate * templ, const gchar * name)
{
  g_return_val_if_fail (GST_IS_PAD_TEMPLATE (templ), NULL);

  return g_object_new (GST_TYPE_PAD,
      "name", name, "direction", templ->direction, "template", templ, NULL);
}

gst_object_unref needs to be ran on the result of gst_static_pad_template_get to avoid leaking this GstPadTemplate.