Consegui corrigir o problema usando o gdisk . Na verdade nenhum outro programa foi capaz de me dizer qual é realmente o problema. É isso:
Found invalid GPT and valid MBR; converting MBR to GPT format in memory. THIS OPERATION IS POTENTIALLY DESTRUCTIVE! Exit by typing 'q' if you don't want to convert your MBR partitions to GPT format!
AND
Warning! Secondary partition table overlaps the last partition by 3657528735 blocks! You will need to delete this partition or resize it in another utility.
O que eu fiz:
Exclua todas as partições no palito:
Command (? for help): d
Partition number (1-4): 1
Command (? for help): d
Partition number (2-4): 2
Command (? for help): d
Partition number (3-4): 3
Command (? for help): d
Using 4
Criar novo MBR
Command (? for help): o
This option deletes all partitions and creates a new protective MBR.
Proceed? (Y/N): y
Verificar disco
Command (? for help): v
No problems found. 31276989 free sectors (14.9 GiB) available in 1
segments, the largest of which is 31276989 (14.9 GiB) in size.
Escreva no disco
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT) to /dev/sdb.
The operation has completed successfully.
Depois disso, consegui formatar o bastão como de costume.