There are two problems here:
1) Shareaza sometimes incorrectly marks a file as ghost. My understanding is that the only way to make a ghost file is to either: 1) cancel a download and choose the ghost option, and 2) delete the file from within Shareaza. Since I never do either 1) or 2), I shouldn't have any ghost files, but Shareaza seems to think that the file was deleted while actually I've merely moved it to another folder. Maybe there's something I don't quite get here.
2) Once the file is marked as ghost, how to remove it from that list? Since it actually exists in the library, deleting a ghost causes the file to be deleted too, which is not what I want. If I save a copy of the file, delete the ghost, then return this copy to its original location, it's again marked as ghost.