This is still a problem in Wily 15.10 (ami-225ebd11)

On the ec2 console I see:

Cloud-init 0.7.7 received SIGTERM, exiting...
  Filename: /usr/lib/python3/dist-packages/cloudinit/config/cc_power_state_change.py
  Function: run_after_pid_gone
  Line number: 209
    Filename: /usr/lib/python3/dist-packages/cloudinit/util.py
    Function: fork_cb
    Line number: 285
      Filename: /usr/lib/python3/dist-packages/cloudinit/config/cc_power_state_change.py
      Function: handle
      Line number: 109

And in /var/log/cloud-init.log:

Oct 28 21:16:14 ubuntu [CLOUDINIT] helpers.py[DEBUG]: Running config-power-state-change using lock (<FileLock using file '/var/lib/cloud/instances/i-ea987333/sem/config_power_state_change'>)
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Reading from /proc/1062/cmdline (quiet=False)
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Read 58 bytes from /proc/1062/cmdline
Oct 28 21:16:14 ubuntu [CLOUDINIT] cc_power_state_change.py[DEBUG]: After pid 1062 ends, will execute: shutdown -P now
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Forked child 1080 who will run callback run_after_pid_gone
Oct 28 21:16:14 ubuntu [CLOUDINIT] handlers.py[DEBUG]: finish: modules-final/config-power-state-change: SUCCESS: config-power-state-change ran successfully
Oct 28 21:16:14 ubuntu [CLOUDINIT] cloud-init[DEBUG]: Ran 11 modules with 1 failures
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Reading from /proc/1062/cmdline (quiet=False)
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Read 58 bytes from /proc/1062/cmdline
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Creating symbolic link from '/run/cloud-init/result.json' => '../../var/lib/cloud/data/result.json'
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Reading from /proc/uptime (quiet=False)
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Read 12 bytes from /proc/uptime
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: cloud-init mode 'modules' took 0.502 seconds (0.50)
Oct 28 21:16:14 ubuntu [CLOUDINIT] handlers.py[DEBUG]: finish: modules-final: FAIL: running modules for final
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Cloud-init 0.7.7 received SIGTERM, exiting...#012  Filename: /usr/lib/python3/dist-packages/cloudinit/config/cc_power_state_change.py#012  Function: run_after_pid_gone#012  Line number: 209#012    Filename: /usr/lib/python3/dist-packages/cloudinit/util.py#012    Function: fork_cb#012    Line number: 285#012      Filename: /usr/lib/python3/dist-packages/cloudinit/config/cc_power_state_change.py#012      Function: handle#012      Line number: 109
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[WARNING]: Failed forking and calling callback run_after_pid_gone
Oct 28 21:16:14 ubuntu [CLOUDINIT] util.py[DEBUG]: Failed forking and calling callback run_after_pid_gone#012Traceback (most recent call last):#012  File "/usr/lib/python3/dist-packages/cloudinit/util.py", line 285, in fork_cb#012    child_cb(*args, **kwargs)#012  File "/usr/lib/python3/dist-packages/cloudinit/config/cc_power_state_change.py", line 209, in run_after_pid_gone#012    time.sleep(.25)#012  File "/usr/lib/python3/dist-packages/cloudinit/signal_handler.py", line 63, in _handle_exit#012    sys.exit(rc)#012SystemExit: 1