Looking through the code, it seems as though you get labels for HTML galleys, PDF, Postscript, XML, Audio, and Slideshow (for powerpoint). These labels are set in PaperGalleyForm.inc.php by looking at the uploaded file type returned by PaperFileManager (which subclasses FileManager). If none of these labels apply, the "Untitled" label is used for the galley display.
Michael has done a lot of work on this, and some of these patches may be useful.http://pkp.sfu.ca/bugzilla/show_bug.cgi?id=6876
Let us know how that works out.