I wanted to use btrfs on my Linux Mint PC more, but I keep encountering new issues. Now I've found out (tried on two USB sticks) that btrfs formatted USB stick can be properly unmounted/ejected via GUI (Nemo), but not from terminal.
$ umount /dev/sdb1 Error finding object for block device 0:87
For other fs it works, just checked that after I insert USB stick and it is automounted, running umount in terminal works (for ext4 and ISO 9660), but not for btrfs.
Sticks were formatted with btrfs via Gnome-disks, maybe it matters...
Btrfs partition on local harddrive mounted via Gnome-Disks GUI produced same error on
umount in terminal. I was able to successfully
sudo mount and
sudo umount it in terminal.
sudo umount works and does not produce the error.