I have a partition with btrfs that already has the subvolumes to
work with snapper, say .snapshots and a few snapper snapshots, e.g.
.snapshots/1/snapshot. The partition is not mounted.

I start YaST to mount the partition. Now YaST does not only add
the main btrfs to fstab but also all subvolumes, e.g. including
.snapshots/1/snapshot. That is not the correct setup for snapper.

Unfortunately this is not just a cosmetic mistake. Using snapper
to delete snapshots now has the effect that the btrfs snapshots
are deleted but not the entries in fstab. This results in a boot
failure next time.