I have no idea ... It is a quirk of LW's searching ability. Also you can put the song and artist name in All types and you will recieve ... for example .as I have just done it ...and got 325 good results.
I put the same artist and song in the relevant boxes of Audio search and got 490 ... only problem here is that about half are for different songs by the same artist .... go figure!
Experiment a bit with searches and you will find what works best for you
