Whoops, found two of them... One in the physical disk backup code (right button on a HD icon in the open disk dialog, not the same as partition sectors backup in the Disk menu), which didn't allow the backups to start anywhere else than at sector 0. The other one was a minor problem with the dragging code in the file list (Unknown file icon displayed when dragging a folder or a musical file).
/!\ Experts only /!\ kids don't try this at home...
I also implemented the MBR Backup / Restore features on the physical disks, it can be useful if you try to make your I-Bead bootable.