[Vorbis] Vorbis encoding at half speed

[Ross Levis]

I’m using a Windows development component which uses vorbis.dll, ogg.dll, vorbisenc.dll for encoding an Ogg Vorbis file.  It's all working well except for one user occasionally has a 1 hour file appear as 2 hours and it plays at half speed.  It is being converted from stereo to mono before feeding the encoder with a channels=1 configuration.

Here is an example file which will be available for a few weeks.
http://stationplaylist.com/temp2398/Hour2.ogg

Any ideas why this should occur sometimes but works fine other times?

Ross.