Btrfs devel - Jul 2014 - `btrfsck: extent_io.c:612: free_extent_buffer: Assertion `!(eb->flags & 1)' failed.` in `btrfsck`

Hi together,
I'm experiencing the following issues when I invoke `btrfsck` on a
sparse file image with a GPT and one (the only) btrfs partition attached
to a loop device

    $ sudo btrfsck --repair --init-csum-tree --init-extent-tree -b
/dev/loop0p1
    Incorrect local backref count on 128510738432 root 5 owner 3849475
offset 0 found 1 wanted 0 back 0xbab41270
    backpointer mismatch on [128510738432 4096]
    ref mismatch on [128510742528 12288] extent item 0, found 1
    btrfsck: extent_io.c:612: free_extent_buffer: Assertion `!(eb->flags
& 1)' failed.

    $ sudo btrfsck --repair --init-csum-tree --init-extent-tree /dev/loop0p1
    Incorrect local backref count on 128510726144 root 5 owner 3849470
offset 0 found 1 wanted 0 back 0xbbcb9500
    backpointer mismatch on [128510726144 12288]
    ref mismatch on [128510738432 4096] extent item 0, found 1
    adding new data backref on 128510738432 root 5 owner 3849475 offset
0 found 1
    Backref 128510738432 root 5 owner 3849475 offset 0 num_refs 0 not
found in extent tree
    Incorrect local backref count on 128510738432 root 5 owner 3849475
offset 0 found 1 wanted 0 back 0xbbcb9630
    backpointer mismatch on [128510738432 4096]
    ref mismatch on [128510742528 12288] extent item 0, found 1
    btrfsck: extent_io.c:612: free_extent_buffer: Assertion `!(eb->flags
& 1)' failed.

    $ sudo btrfsck --repair /dev/loop0p1
    Incorrect local backref count on 130861096960 root 5 owner 22733727
offset 0 found 1 wanted 0 back 0xc7c7d170
    backpointer mismatch on [130861096960 8192]
    ref mismatch on [130861105152 8192] extent item 0, found 1
    btrfsck: extent_io.c:612: free_extent_buffer: Assertion `!(eb->flags
& 1)' failed.

    $ sudo btrfsck --repair /dev/loop0p1
    Backref 130861096960 root 5 owner 22733727 offset 0 num_refs 0 not
found in extent tree
    Incorrect local backref count on 130861096960 root 5 owner 22733727
offset 0 found 1 wanted 0 back 0xc7f31170
    backpointer mismatch on [130861096960 8192]
    ref mismatch on [130861105152 8192] extent item 0, found 1
    btrfsck: extent_io.c:612: free_extent_buffer: Assertion `!(eb->flags
& 1)' failed.

I'm using `btrfs-progs` 24cf4d8c3ee924b474f68514e0167cc2e602a48d on
Linux 3.16-rc5 (anything else, i.e. older versions, give me immediate
error after start because errornous file system)

I'd like to know whether this (assertion) error is related to a bug or
missing feature in btrfs-progs and might be fixed at some point or
whether this might indicate a completely messed up btrfs.

Best regards,
Karl-P. Richter