Beats me... it should only show junk according to your preferences
I guess you could try 'forget training data' & apply. Or change the sensitivity.
If you've never labelled anything as junk then I don't know how it's recognising 'junk'.

You could also try deleting your preferences folder while LW's closed (points 2 & 3 below)
Fixes for LimeWire

Then search for a file that you know displayed lots as junk before & see how the results look.

Someone else might know more...