I am actually not so firm with fdisk command(s) anymore because of using gparted mostly
partition would be in use
would (perhaps) say that these partitions are mounted. See man df , fdisk (-l) or /etc/mounts for it.
Some utilities only work when the partition is kept u(n)mount(ed) (man umount).
It sounds a little confusing that work can be done one something that is not mount(ed).
Pretty sure that could be the case here.