Description of problem:
When downloading a bittorrent file to a btrfs filesystem the file contents is sometimes padded by nulls. 

Version-Release number of selected component (if applicable):
Fedora 14
kernel-2.6.35.10-74.fc14.x86_64
transmission-common-2.11-2.fc14.x86_64
transmission-gtk-2.11-2.fc14.x86_64

How reproducible:
Reproducible every time.

Steps to Reproduce:
1. Type
dd if=/dev/zero of=/dev/shm/btrfs.fs count=400 bs=1M
mkfs.btrfs /dev/shm/btrfs.fs
mkdir /dev/shm/btrfs
/bin/su -c "mount -o loop /dev/shm/btrfs.fs /dev/shm/btrfs; chown 777 /dev/shm/btrfs/"

(this should make a btrfs filesystem if you have btrfs-progs)
2. Run
transmission-gtk http://download2.bittornado.com/download/BitTornado-0.3.18-w32install.exe.torrent
(or whatever the "download via BitTorrent" link on http://www.bittornado.com/download.html is)
3. In the "Torrent Options" window set the Destination Folder to /dev/shm/btrfs/ .
4. Wait for the file to fully download.
5. Run
md5sum /dev/shm/btrfs/BitTornado-0.3.18-w32install.exe

(or whatever the downloaded file was called)
  
Actual results:
161c85a87dc0d973526a4a066abb4f83  /dev/shm/btrfs/BitTornado-0.3.18-w32install.exe

tail -c 1800 /dev/shm/btrfs/BitTornado-0.3.18-w32install.exe | hexdump
0000000 cef4 9d15 e5eb aee4 1691 97fc bd80 b7ed
0000010 9df7 fab2 427f 6896 6d37 a3ed eeff 6851
0000020 dcb8 a5f0 00bc 0000 0000 0000 0000 0000
0000030 0000 0000 0000 0000 0000 0000 0000 0000
*
0000700 0000 0000 0000 0000                    
0000708

Expected results:
0783ba53b308f400883a94d2da4cecb4  /dev/shm/btrfs/BitTornado-0.3.18-w32install.exe
(or whatever the hash on http://www.bittornado.com/download.html says)

tail -c 37 /dev/shm/btrfs/BitTornado-0.3.18-w32install.exe | hexdump 
0000000 cef4 9d15 e5eb aee4 1691 97fc bd80 b7ed
0000010 9df7 fab2 427f 6896 6d37 a3ed eeff 6851
0000020 dcb8 a5f0 00bc                         
0000025

Additional info:
Using an ext4 or tmpfs filesystem does not show the problem.