After the big courtyard fight where you save Sully with a bunch of grenades he just decided to levitate around some. After loading my save I wound up in a fantastic white room. XD

   
I found this after completing The Truth level in the Animus. It happened during the cutscene, which I wish I had took a video of but I was laughing to much at how ridiculous it was. Basically Desmond got caught in some weird animation loop when trying to get out of the chair and than after the cutscene clipped through the Animus.