It happened once that they sort of got carried away during the Zappa Jam in BTL-2004, and followed a faster and faster upwards spiral until they literaly ran out of notes in their instruments to play. So they just stoppe dead for like 5 seconds before reprising the jam on a more somber and funky note.
The audience approved and so do I, incredible live moment!
EDIT: I may actually upload a video of that, it's a very obscure live moment I think should be better known among DT fans!