[del]I did re-download the files a second time, but since they are from a .zip, the contents should be checked on export.
[del]I downloaded them from the humble site three times now - number 3 always 'skips'.
[del]Very odd that it's my machine - I'll do some checking with a different player and see if that helps. Odd that the rest are fine (WAV and MP3, just not flac).[/del]
[del]Thanks for the responses.[/del]
Sigh. It's a bug in VLC 2.1.1. Upgraded to 2.1.2 and it's all fine now. Many thanks!