problem with identify -format %c

I'm having a problem with identify -format %c (and %l): it is not properly outputting
the label or comment.

I ran this small test:

convert -comment abcdef logo: png:- | identify -format %c png:-

On newer versions of imagemagic the command fails (returns a blank line),
on older versions it works.

centos 5.3 (6.2.8): works (prints abcdef)
fedora 10 (6.5.1-2) fails (blank line)
gentoo 6.4.0: works (prints abcdef)
gentoo 6.5.1-0 fails (blank line)
gentoo 6.5.2-9: fails (blank line)

The problem seems to be with the 'identify' program, not with
convert: I saved the output of convert and tried it on various
systems; it didn't matter what the version of convert was, just
the version of identify.

running identify -verbose on the image shows the comment in the Properties
section; its just '-format %c' that is broken.