what version of FLAC are you using?
xact is 1.59 and i tried frontend 1.2.1 -- and after reading a thread you wrote; something on flac and the legacy file issue (got to searching because my foobar would not play these flacs -- "unsupported or corrupt"), i shitcanned that one and found an older version = 1.2.0 still the same problem -- won't work in dvd audiofile. but the problem here, and what's making me think it's the file itself is that even when i take the copied file from the 744 and and try to make an .iso from that (should still work, and has, even though dvd-audiofile likes flac), it flies through the process and leaves me with a 20 kb or so image.
i am able to decode those flacs and play/edit the wavs in foobar, audacity, cdwav.. just not in the dvd audio tool.