Hi there, I have had what I believe is the same problem when I someone has created a document and exported as a PDF, but for some reason or another they have changed the name of the file in the 'Save as' field. For example, you have a file called 'Document 1' and when you go to export it to PDF you change the name in the 'Save as' field to 'Document XX.pdf' and export it, it will retain 'Document XX.pdf' whenever you export it, you can even duplicate the document, change its name and when you go to export it, it will still have 'Document XX.pdf'! I think this is really bad but some may find it useful.
Anyway, the only way I have found to change this (there maybe more sophisticated or more efficient ways, this is just how I get over the problem) is to either change the name in the 'Save as' field to what it should be, which is what caused the problem to begin with, or you can export the document as an INX, reopen it, save it with the correct filename and then export as a PDF. Then even if you copy the document and rename the document in the finder, it will export with the correct filename.
I hope this helps, sorry for waffling on if this has nothing to do with your problem. Oh and if you go to export (OS X), if you click on another file in the dialogue box, it will copy that filename, but I don't think that's the issue.
Mark