If you have audacious installed, gnome wants to open all plugged usb thumb drives with audacious instead of the file manager. I haven't found a way to change this and recommend to remove the mime type from audacious' desktop entry. This also happens in Cauldron alpha2.
I just filed this bug. I think this is related, hope it helps. ;-) https://bugs.mageia.org/show_bug.cgi?id=10117
CC: (none) => ezequiel_partida
resolve as dup then *** This bug has been marked as a duplicate of bug 10117 ***
Status: NEW => RESOLVEDResolution: (none) => DUPLICATE