does not use the '--' to stop parsing switches

How to reproduce:
$ mkdir -p /tmp/a ; cd /tmp/a
$ for f in alpha beta -delta; do convert -size 100x100 xc: +noise Random -- $f.png; done
$ montage -- *.png gamma.jpg

Expected behaviour:
( image gamma.jpg is created )

Observed behaviour:
"montage: unrecognized option `-delta.png' @ error/montage.c/MontageImageCommand/865."

What's weird is I'd expect convert to throw a similar exception when I execute:

$ convert -size 100x100 xc: +noise Random -delta.png

but it doesn't. This is what I get instead when I use '--' to stop parsing switches:

$ convert -size 100x100 xc: +noise Random -- -delta.png
convert: missing an image filename `-delta.png' @ error/convert.c/ConvertImageCommand/3009.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: imagemagick 8:6.6.9.7-5ubuntu3.2
ProcVersionSignature: Ubuntu 3.2.0-25.40-generic-pae 3.2.18
Uname: Linux 3.2.0-25-generic-pae i686
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu13
Architecture: i386
Date: Fri Sep 14 10:51:14 2012
ProcEnviron:
 LANGUAGE=en_CA:en
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_CA.UTF-8
 SHELL=/bin/bash
SourcePackage: imagemagick
UpgradeStatus: Upgraded to precise on 2012-04-28 (139 days ago)