Hi,
The percentage shown in the %played columns of my one-file audiobooks longer than six hours (or, as I noted in the title, 5:57:54) gets reset to 1% at exactly that same point, and remains at it until the end of the book. Also, for a few long one-file audiobooks in my library the percentage is not shown at all. The %played feature works flawlessly for all other audiobooks, as long as the duration of the audio doesn't exceed 6 hours.
The last played positions are remembered normally, so this doesn't cause much inconvenience (except when the audiobook contains several such files, in which case on resuming the audiobook one needs to guess which file had been played last. )