I will try to get you a log of this -- it usually happens if I've been doing other things first, then try to create/save a new dialog chunk. It always works if I close down, reopen and enter the dialog chunk first thing.
(Also of note, if dialog hasn't saved the chunk, it will give me an error when the game tries to pull up the chunk. If I go back to the dialog extension before closing, the "missing" chunk will be there, but if I close down and re-open, the missing dialog chunk is gone.)