Something like that is happening to me here, too.
At first, I've imported my iTunes library, and all of my songs had on the track number field.
I thought it could be something related to the way iTunes creates its library, so I uninstalled Winamp completely, removing preference files, cache etc, the lot. Afterwards, I reinstalled it and imported my mp3 folder directly into it, but it didn't work. The dreaded "UndefinedKeyValue" remains.
Without track order, I might as well just drag the original mp3 files straight into Android File Transfer. At least I know that works.
UPDATE: switched to the Beta channel according to the instructions from the Labs page,
and still no success. Track# is now 0 for all my files.