It may be a bug - there is currently an issue where, if the keyboard is displayed when you tap to load a song, it reduces the height available for rendering the file and MobileSheets renders to that size. Then the keyboard is hidden bringing back the additional height but MobileSheets doesn't force the song to layout the pages again. I am releasing a fix for this today. I apologize for any inconvenience this has caused. If you close the virtual keyboard before loading the song, it should display just fine.
Mike
Mike