$ dd if=/dev/zero of=block bs=1k count=5760
$ mke2fs -F block
$ cat repro.py 
from kobo.shortcuts import run
from pungi.util import temp_dir
import os
with temp_dir() as mount_tmp_dir:
    run(["LIBGUESTFS_BACKEND=direct", "guestmount", "-a", "block", "-m", "/dev/sda", mount_tmp_dir])
    print os.listdir(mount_tmp_dir)
    run(["fusermount", "-u", mount_tmp_dir])
$ python repro.py
['lost+found']
Traceback (most recent call last):
  File "repro.py", line 9, in <module>
    run(["fusermount", "-u", mount_tmp_dir])
  File "/home/lsedlar/repos/kobo/kobo/shortcuts.py", line 337, in run
    raise exc
RuntimeError: ERROR running command: fusermount -u /tmp/tmpMlB24G