FLAC DirectShow source filter outputs wrong number of samples

When using the opencodecs 0.85.17777 DS source filter to decode FLAC files, the resulting length is too short. This has been going on for a long time (back to the illiminable days), but I just found out it was happening (and causing problems).

I'm on WinXP SP3 (32-bit). The FLAC files are all compressed with the latest libFLAC (1.2.1) tools at compression level 8.

I first decoded a FLAC file to WAV using flac.exe. I then used Graphstudio (you can use Graphedit instead) to send a FLAC file to the WAVDEST filter, then a file output filter. When the source filter was the Xiph filter, the resulting WAV file was too short (around 3% smaller than it should be).

When I did the same thing using the madFlac source filter, the resulting WAV file was precisely the right length.