In case when there is a teletext subtitle and there is no succeeder subtitle the text is displayed too long on screen. In addition the subtitles are all displayed in blue. White is a better choise.
Currently on Discovery HD for the Netherlands has subtitles in Teletext and DVB. Both you can select, but nothing is displayes while a TopField receiver does show them. These subtitles are most likely a plan to share Discovery HD with SkyLink.