High memory usage when converting to monochrome

Roxis <[email protected]> Fri, 23 Jul 2010 10:04:54 +0400
Newsgroups gmane.comp.video.image-magick.bugs
Message-ID <[email protected]>
When converting image of any size to a monochrome one
I get 64M+ memory usage

how to reproduce:
strace -e munmap convert any-image.png -monochrome out.png

> ...
> munmap(0xb32f7000, 67112960)            = 0
> ...

tested on CentoOS 5.5 with self builded 6.5.7-7, 6.6.3-0 and 6.5.7.7-1.i686.rpm 
from http://yum.cocoiti.com/CentOS/5/RPMS/i686/