automount segfaults when auto.master "dir" points to a file

Given an auto.master file with the following line:

# cat /etc/auto.master
+dir:/etc/auto.master.d

and /etc/auto.master.d is a file:

# stat /etc/auto.master.d
  File: ‘/etc/auto.master.d’
  Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: fc00h/64512d Inode: 6817460 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2014-11-07 23:54:42.640848261 +1100
Modify: 2014-11-07 23:54:42.640848261 +1100
Change: 2014-11-07 23:54:42.640848261 +1100
 Birth: -

the autofs service fails to start due to multiple segfaults:

# service autofs start & tail -F /var/log/syslog
autofs start/running, process 4157
Nov 9 20:56:11 europa kernel: [ 641.836878] show_signal_msg: 1 callbacks suppressed
Nov 9 20:56:11 europa kernel: [ 641.836885] automount[4157]: segfault at 0 ip 00007f7c3bbc8920 sp 00007fff9f158768 error 4 in libc-2.19.so[7f7c3bb0b000+1bb000]
Nov 9 20:56:11 europa kernel: [ 641.839921] init: autofs main process (4157) killed by SEGV signal
Nov 9 20:56:11 europa kernel: [ 641.839943] init: autofs main process ended, respawning
Nov 9 20:56:11 europa kernel: [ 641.916675] automount[4166]: segfault at 0 ip 00007fad88d51920 sp 00007fff7bbecc28 error 4 in libc-2.19.so[7fad88c94000+1bb000]
Nov 9 20:56:11 europa kernel: [ 641.918773] init: autofs main process (4166) killed by SEGV signal
Nov 9 20:56:11 europa kernel: [ 641.918788] init: autofs main process ended, respawning
Nov 9 20:56:11 europa kernel: [ 641.968632] automount[4175]: segfault at 0 ip 00007f0ee3fca920 sp 00007fff02ab3308 error 4 in libc-2.19.so[7f0ee3f0d000+1bb000]
Nov 9 20:56:11 europa kernel: [ 641.970738] init: autofs main process (4175) killed by SEGV signal
Nov 9 20:56:11 europa kernel: [ 641.970753] init: autofs main process ended, respawning
Nov 9 20:56:11 europa kernel: [ 642.040704] automount[4184]: segfault at 0 ip 00007fc953493920 sp 00007fffec2dc0e8 error 4 in libc-2.19.so[7fc9533d6000+1bb000]
Nov 9 20:56:11 europa kernel: [ 642.043116] init: autofs main process (4184) killed by SEGV signal
Nov 9 20:56:11 europa kernel: [ 642.043133] init: autofs main process ended, respawning
Nov 9 20:56:11 europa kernel: [ 642.104755] automount[4193]: segfault at 0 ip 00007f968326d920 sp 00007fff44edcc18 error 4 in libc-2.19.so[7f96831b0000+1bb000]
Nov 9 20:56:11 europa kernel: [ 642.107902] init: autofs main process (4193) killed by SEGV signal
Nov 9 20:56:11 europa kernel: [ 642.107919] init: autofs main process ended, respawning
Nov 9 20:56:12 europa kernel: [ 642.176779] automount[4202]: segfault at 0 ip 00007f03aebb1920 sp 00007fffe76345c8 error 4 in libc-2.19.so[7f03aeaf4000+1bb000]
Nov 9 20:56:12 europa kernel: [ 642.179081] init: autofs main process (4202) killed by SEGV signal
Nov 9 20:56:12 europa kernel: [ 642.179099] init: autofs main process ended, respawning
Nov 9 20:56:12 europa kernel: [ 642.236726] automount[4211]: segfault at 0 ip 00007f9f446c4920 sp 00007fff260533d8 error 4 in libc-2.19.so[7f9f44607000+1bb000]
Nov 9 20:56:12 europa kernel: [ 642.238905] init: autofs main process (4211) killed by SEGV signal
Nov 9 20:56:12 europa kernel: [ 642.238922] init: autofs main process ended, respawning
Nov 9 20:56:12 europa kernel: [ 642.308743] automount[4220]: segfault at 0 ip 00007f9929fb7920 sp 00007fffba052698 error 4 in libc-2.19.so[7f9929efa000+1bb000]
Nov 9 20:56:12 europa kernel: [ 642.311101] init: autofs main process (4220) killed by SEGV signal
Nov 9 20:56:12 europa kernel: [ 642.311119] init: autofs main process ended, respawning
Nov 9 20:56:12 europa kernel: [ 642.372656] automount[4229]: segfault at 0 ip 00007f1342759920 sp 00007fff68610ff8 error 4 in libc-2.19.so[7f134269c000+1bb000]
Nov 9 20:56:12 europa kernel: [ 642.374811] init: autofs main process (4229) killed by SEGV signal
Nov 9 20:56:12 europa kernel: [ 642.374826] init: autofs main process ended, respawning
Nov 9 20:56:12 europa kernel: [ 642.424646] automount[4238]: segfault at 0 ip 00007fa402eb2920 sp 00007fffb89266e8 error 4 in libc-2.19.so[7fa402df5000+1bb000]
Nov 9 20:56:12 europa kernel: [ 642.426643] init: autofs main process (4238) killed by SEGV signal
Nov 9 20:56:12 europa kernel: [ 642.426658] init: autofs main process ended, respawning
Nov 9 20:56:12 europa kernel: [ 642.495381] init: autofs main process (4247) killed by SEGV signal
Nov 9 20:56:12 europa kernel: [ 642.495397] init: autofs respawning too fast, stopped

While I'm sure that autofs should fail under these circumstances (I certainly don't know how I managed to make auto.master.d a file), I'm not sure that segfaults should occur.

# apt-cache policy autofs
autofs:
  Installed: 5.0.7-3ubuntu3.1
  Candidate: 5.0.7-3ubuntu3.1
  Version table:
 *** 5.0.7-3ubuntu3.1 0
        500 http://mirror.as24220.net/pub/ubuntu-archive/ trusty-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     5.0.7-3ubuntu3 0
        500 http://mirror.as24220.net/pub/ubuntu-archive/ trusty/main amd64 Packages

# lsb_release -a
No LSB modules are available.
Distributor ID: LinuxMint
Description: Linux Mint 17 Qiana
Release: 17
Codename: qiana