I doubt the format has ever been published. There have been a few people who have tried to decode it, e.g. http://www.andrewj.com/mft/mftproject.asp, and they have only found 32 byte records (actually 16 fields of 2 bytes each).
Since the value of the fields seems to be preserved, it seems as though some directory length is not being preserved, rather than the metadata itself being trashed.