x11vnc crashes when using the -env FD_XDM=1 -auth guess switch

[cleary]

x11vnc fails to start with the following command:
  /usr/bin/x11vnc -inetd -q -env FD_XDM=1 -auth guess -display :0 -unixpw root

It starts if you leave off the -auth guess (but won't allow connection)

Removing -env FD_XDM=1 AND -auth guess starts cleanly, and allows connection

This behaviour has changed since 20140626, which is when it most recently worked for me (and had been working for ~5 years prior to that).
x11vnc hasn't updated, but several of it's ssl dependencies have, as well as libc6.

Ubuntu 14.04 (up to date)
ii x11vnc 0.9.13-1.1 amd64 VNC server to allow remote access to an existing X session
ii x11vnc-data 0.9.13-1.1 all data files for x11vnc

x11vnc
  Depends: openssl *changed since 20140626
  Depends: tk
  Depends: x11vnc-data
  Depends: libavahi-client3
  Depends: libavahi-common3
  Depends: libc6 *changed since 20140626
  Depends: libssl1.0.0 *changed since 20140626
  Depends: libvncserver0 *changed since 20140626
  Depends: libx11-6
  Depends: libxdamage1
  Depends: libxext6
  Depends: libxfixes3
  Depends: libxinerama1
  Depends: libxrandr2
  Depends: libxtst6

strace sample (complete broken trace attached):
Non-working:

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f916df28000
read(3, "", 4096) = 0
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=4794, si_status=0, si_utime=0, si_stime=0} ---
close(3) = 0
wait4(4794, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 4794
munmap(0x7f916df28000, 4096) = 0
shmdt(0) = -1 EINVAL (Invalid argument)
shmctl(0, IPC_RMID, 0) = -1 EIDRM (Identifier removed)
shmdt(0) = -1 EINVAL (Invalid argument)
shmctl(0, IPC_RMID, 0) = -1 EIDRM (Identifier removed)
shmdt(0) = -1 EINVAL (Invalid argument)
shmctl(0, IPC_RMID, 0) = -1 EIDRM (Identifier removed)
exit_group(1) = ?
+++ exited with 1 +++

==============================================

Working (20140626 build):

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fec98926000
read(3, "XAUTHORITY=/var/run/xauth/A:0-jK"..., 4096) = 37
read(3, "", 4096) = 0
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=2833, si_status=0, si_utime=0, si_stime=0} ---
close(3) = 0
wait4(2833, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 2833
munmap(0x7fec98926000, 4096) = 0
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC, 0) = 3
connect(3, {sa_family=AF_LOCAL, sun_path=@"/tmp/.X11-unix/X0"}, 20) = 0
getpeername(3, {sa_family=AF_LOCAL, sun_path=@"/tmp/.X11-unix/X0"}, [20]) = 0
uname({sys="Linux", node="bilgtit6", ...}) = 0
access("/var/run/xauth/A:0-jKLcZb", R_OK) = 0
open("/var/run/xauth/A:0-jKLcZb", O_RDONLY) = 4
fstat(4, {st_mode=S_IFREG|0600, st_size=44, ...}) = 0
...

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