Thank you Cyan, it works great for me. USBLGX reads config file from my HDD with this mod, even if my SDCard is inserted.
ps : one question which has nothing to do with bugs
Is there a little chance that you add officially, one day, some kind of tab mod (I don't remember who made it the first time, but I used it and tweaked the sources to compile my own version of USBLoader GX, see below) ?
I'm using devkitPPC_r26 and Libogc1.8.12
It currently doesn't compile with devkitPPC_r27, it needs a lot of fixes. (it can only work better after that!)