'tain c'est bizarre, je lance un partprobe et j'ai ça :
Warning: /dev/sdb contains GPT signatures, indicating that it has a GPT table. However, it does not have a valid fake msdos partition table, as it should. Perhaps it was corrupted -- possibly by a program that doesn't understand GPT partition tables. Or perhaps you deleted the GPT table, and are now using an msdos partition table. Is this a GPT partition table?
Error: The backup GPT table is corrupt, but the primary appears OK, so that will be used.
Error: Partition(s) 1 on /dev/sdb have been written, but we have been unable to inform the kernel of the change, probably because it/they are in use. As a result, the old partition(s) will remain in use. You should reboot now before making further changes.
J'ai jamais eu ça avant. 
Je lance quand même gParted ?