mkfs.btrfs failed with new, ok with old

~peter/projects/btrfs-progs/mkfs.btrfs -L usb3test -d raid0 -m raid0 /dev/sdb1 /dev/sdc1

WARNING! - Btrfs v0.20-rc1-37-g91d9eec-dirty IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using

error checking /dev/sdb1 mount status


# mkfs.btrfs -L usb3test -d raid0 -m raid0 /dev/sdb1 /dev/sdc1

WARNING! - Btrfs v0.19+20120406 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using

adding device /dev/sdc1 id 2
fs created label usb3test on /dev/sdb1
        nodesize 4096 leafsize 4096 sectorsize 4096 size 59.40GiB
Btrfs v0.19+20120406


# strace ~peter/projects/btrfs-progs/mkfs.btrfs -L usb3test -d raid0 -m raid0 /dev/sdb1 /dev/sdc1
...
stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
stat("/dev/sdb1", {st_mode=S_IFBLK|0660, st_rdev=makedev(8, 17), ...}) = 0
stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
open("/dev/loop0", O_RDONLY)            = 5
ioctl(5, LOOP_GET_STATUS, 0x7fff5526c700) = 0
close(5)                                = 0
lstat("/dev", {st_mode=S_IFDIR|0755, st_size=5180, ...}) = 0
lstat("/dev/sdb1", {st_mode=S_IFBLK|0660, st_rdev=makedev(8, 17), ...}) = 0
lstat("/home", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/home/peter", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/home/peter/archive", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/home/peter/archive/software", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/home/peter/archive/software/openSUSE", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0
lstat("/home/peter/archive/software/openSUSE/Peters_LiveCD_KDE4_kernel", 0x7fff5526a5b0) = -1 ENOENT (No such file or directory)
close(4)                                = 0
munmap(0x7f7e6b7b9000, 4096)            = 0
close(3)                                = 0
write(2, "error checking /dev/sdb1 mount s"..., 38error checking /dev/sdb1 mount status
) = 38
exit_group(1)                           = ?