Cerrot, when checking your hard drive in your music folder (the folder that either lists the artists in sub-folders, typical with further sub-folders by album) you are seeing, for example that tracks 1-3 and 5-9 are there, but for some reason track 4 is not?
Sometimes, these tracks show up in other folders, for the reasons I stated above (different artist listing, or song with "featuring . . . "). Sometimes these tracks or songs can show up in other folders, such as various artists, unknown artists, compilations, etc. . .
In my case, these tracks can then be dragged and dropped back to where I want them. Or more often, when ripping the CD, I will review the list of songs and artists (by song). Songs that have for example, "Frank Sinatra, feat. you name the other singer", I will modify and rename the artist as just "Frank Sinatra" in this case. This assures me that the song is kept or put where it should be.
There, I believe, are setting that can be made that allows such songs to be kept under the primary artists name, but again, this sometimes depends on how the artists are listed.
Hope this helps, but then again, you issue may be completely different. Sounds like you got it covered anyway with dBPower, but perhaps helpful to others.