My idea was that (using loopback devices) it works like this

1. Create the raid array sudo mkfs.btrfs -m raid1 -d raid1 /dev/loop1 /dev/loop2
2. You mount them sudo mount /dev/loop1 /mnt and mark them touch goodcondition
3. You unmount and simulate disk failure (remove disk or delete loopback device loop2 in my case)
4. You mount degraded -o degraded and mark again touch degraded
5. You add the bad disk again sudo btrfs dev add /dev/loop2
6. You rebalance sudo btrfs fi ba /mnt

And Raid 1 should work again. But that's not the case. sudo btrfs fi show:

Total devices 3 FS bytes used 28.00KB
devid    3 size 4.00GB used 264.00MB path /dev/loop1
devid    2 size 4.00GB used 272.00MB path /dev/loop2
*** Some devices missing

The file degraded lives on loop1 but not on loop2 when loop2 is mounted in degraded mode. Why is that?