Loss of audio sync on MP4 playback with [network-shares-automount]

[Mick]

Hi all - I've converted a series of DVDs to .mp4 files with Handbrake and, using [network-shares-automount], I view them across my network on my Humax HDR. However, one has out-of-sync audio when played on the Humax but is fine when played directly on a PC.
Any ideas on why only one of several should play up? All DVDs are UK PAL ones, and some from the same company too.

Thanks
Mick