xdg-open error when opening a mounted folder in root

Hi,
on Ubuntu 11.04, when using "sudo xdg-open /myfolder" (or gksu instead of sudo) to open a folder:
- it opens the folder correctly with Nautilus except in the case below:
- when the folder is a mounted partition ( /dev/sdXY ) or a mount point ( /media/mymountpoint ), it opens an audio player (!?!) and I get the error below :

Warning: unknown mime-type for "/media/Perso" -- using "application/octet-stream"
Error: no "view" mailcap rules found for type "application/octet-stream"
Opening "/media/Perso" with Decibel Audio Player (inode/mount-point)

PS: I read in the man that "It is not recommended to use xdg-open as root.", so maybe this bug is already known. And FYI I need to use xdg-open as root because I develop a GNU-GPL software (Boot-Repair) which is started via gksu, and I need to use xdg-open inside this app :)

Best regards