I don't get it. It's been over two years since Windows phone 8. And still there is no fix for the other storage issue. What is taking Microsoft so long??? It's really irritating that 2-3 gigs of internal memory is going wasted this way.
Plug your phone via USB into a Windows 8.1 box and open the Windows Phone (Metro UI) App. It will reindex your card and you might find those "other" files are actually your media.
I noticed WP does this with drag and drop straight to SD...