I havent set anything to junk, and I told it to 'Forget Training Data'. When I type in a song and hit search, all of the most popular results are at the bottom and labeled as junk. I downloaded one and scanned it as well, and the whole song played fine with no bad quality at all. It was also a standard size for an MP3, no 350 kb crap. I know I might get a response like "Then just download the junk ones" but I'm asking why it does this, and how can I make it so it doesnt?

This just happened today as well.

Try deleting the LW preferences folder when LW's closed, see points 2 & 3 below
Fixes for LimeWire

This will kill all of your settings within options, you'll have to go back through & reset things afterwards. Then you can set up your junk filter again & hopefully, it will work properly
The thread below has lots of info about using the filter
Junk filter