complete downloads not in libraray???

i have been running LW 2.5 on OS X for about a month with no problems. now for some reason when i download MP3's they will show as complete in the search tab, but when i look in the library they are not all there. i even search the HD w/ sherlock for the mising mp3 but no luck. the weird thing is this doesn't happen to every MP3 every time(more like 25%). i have it downloading to the proper location, i have re-downloaded the same MP3 (which works but only sometimes), i have done anything i can think of besides re-installing (which i would like to avoid). does anyone know what my problem might be. thanks