I have an iPod video(5.5g) running Rockbox 3.13.
When icons are enabled, it will show a video icon on a text file, and on a mess of .m4a files only about half of them will show icons, and the half that do are generic icons, not audio icons.
I currently have icons disabled(reenabled to no sucess) and personally have no need for them. I only posted this to see if anyone else had the issue, and if it needs fixing.