Why does deleting a snapshot increase the used space on btrfs filesystem?
# time ./transaction-test.sh
DEBUG 452 work_begin: before snapshot creation
DEBUG 452 snapshot_create: before sync
DEBUG 408 snapshot_create: before snapshot creation
DEBUG 412 snapshot_create: after snapshot creation
DEBUG 412 work_begin: before changing pwd
DEBUG 412 work_begin: after changing pwd
DEBUG 412 do_test: before test