I'm going to need more information on what process you used to export the placeholder. I selected a placeholder song, tapped Share->Export files, and on the export settings dialog, it has a field where you can enter the name you want to use. The file that was produced was named exactly as I had specified. I also need to know what version of MobileSheets you are running which you can find under Settings->About.
Thanks,
Mike
Thanks,
Mike