kernel BUG at /build/buildd/linux-2.6.38/fs/btrfs/disk-io.c:2349!

I format USB-flash-drive to btrfs, mount it to /media/something. Then I extract USB-flash-drive (while it still mounted). Next second kernel oops happens.
After reboot (and auto-mount USB-flash-drive) I extract it once more (not unmounting), black screen and kernel oops.
Then I format it to ext4, mount and extract, all ok. So only btrfs affected.

ProblemType: KernelOops
DistroRelease: Ubuntu 11.04
Package: linux-image-2.6.38-7-generic 2.6.38-7.38
Regression: No
Reproducible: Yes
ProcVersionSignature: Ubuntu 2.6.38-7.38-generic 2.6.38
Uname: Linux 2.6.38-7-generic i686
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.23.
Annotation: Your system might become unstable now and might need to be restarted.
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: hiint 1686 F.... pulseaudio
CRDA: Error: [Errno 2] Нет такого файла или каталога
Card0.Amixer.info:
 Card hw:0 'NVidia'/'HDA NVidia at 0xfcf78000 irq 20'
   Mixer name : 'Realtek ALC662 rev1'
   Components : 'HDA:10ec0662,18493662,00100101'
   Controls : 34
   Simple ctrls : 18
Date: Thu Mar 24 17:12:24 2011
Failure: oops
HibernationDevice: RESUME=UUID=60049404-b04e-42e5-847b-5a8e6e7a7f51
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Alpha i386 (20110302)
IwConfig:
 lo no wireless extensions.

 eth0 no wireless extensions.

 vboxnet0 no wireless extensions.
MachineType: To Be Filled By O.E.M. To Be Filled By O.E.M.
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.38-7-generic root=UUID=1803f0fb-e456-4836-b304-5ee47c0b26a9 ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-2.6.38-7-generic N/A
 linux-backports-modules-2.6.38-7-generic N/A
 linux-firmware 1.49
RfKill:

SourcePackage: linux
Title: kernel BUG at /build/buildd/linux-2.6.38/fs/btrfs/disk-io.c:2349!
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/22/2009
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: P1.20
dmi.board.name: K10N78M Pro
dmi.board.vendor: ASRock
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP1.20:bd10/22/2009:svnToBeFilledByO.E.M.:pnToBeFilledByO.E.M.:pvrToBeFilledByO.E.M.:rvnASRock:rnK10N78MPro:rvr:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.name: To Be Filled By O.E.M.
dmi.product.version: To Be Filled By O.E.M.
dmi.sys.vendor: To Be Filled By O.E.M.