Keep Circulating the Tapes: Since the Savile sex abuse scandal broke, the BBC has announced it will no longer show reruns of any of his TOTP episodes, rendering a substantial chunk of the surviving run this. Going forward, the only place to watch footage of Savile-era episodes is likely those uploaded to video-sharing services (including those uploaded prior to the ITV-aired exposť).
Missing Episode - Most early episodes of TOTP were wiped by The BBC; only four complete episodes exist from the 1960s (one and most of another with the presenter's links mute), and the show's archive only exists in full from 1977 onwards. And as mentioned above, much of that is now banned.
Too Soon: The BBC's reasoning behind dropping all episodes featuring Savile and/or Dave Lee Travis (who was arrested as part of the Scotland Yard investigation of Savile's crimes) from the BBC Four rerun rotation. The question is whether it will ever stop being too soon.