GstBaseSrc does basically:

static gboolean
gst_base_src_check_get_range (GstPad * pad)
{
  if (!GST_OBJECT_FLAG_IS_SET (src, GST_BASE_SRC_STARTED)) {
    gst_base_src_start (src);
    gst_base_src_stop (src);
  }

  return src->random_access;
}

which means that whenever there's a typefind element involved (ie. always when used via playbin/decodebin), the source device will be opened/closed once just to check whether direct access is possible.

That's bad, especially when the open/close is expensive, like in the case of dvd:// or cdda:// access.

In the case of http, connecting twice to a http server within a very short period of time might lead to the connection being refused on the second (real) attempt (see bug #331690).

The solution for dvd/cdda sources is simple - they can just set up a new checkrange function of their own on the pad that always returns FALSE.

For something like GnomeVfsSrc it's not that straight-forward, as things depend on the URI protocol. Of course it could be hacked around, but I think it's a general problem that should be addressed in GstBaseSrc, maybe by adding a new vfunc.