Its not a bug LB scans your files if you have a merged set you have way less files for it to scan how can it find files you don't have? If you have split or non-merged set these files exist separately and not as pieces combined as one like they do with the merged set so the program can actually see them scan them and add them accordingly based on the criteria that you use. I'm actually unsure as to what running a merged set through import and using the import clones additional apps feature does since the feature is newer.