Recent uploaders to 4Shared may find that the last 4 secs or so of their upload is missing. This can also happen at the beginning but is not so common.
Dont know why this is but a temporary solution would be to add a few secs onto the end of each track.
ALTERNATIVELY - why not give SOUNDCLICK a try. Its more Band inclinated and not quite so user friendly until you get used to it, but its not a bad site for storage and you can copy the Song/Tune URL into your ShadowMusic post just as you do now.
Advantage is that it is also picked up by Radio Stations (mostly USA) and I have found a couple of my tracks (What Do I Do With My Heart and Alentejo being played on them - BIZARRE!!).
Worth a thought.
cheers
ian