Extracting a single page from a post script file

Hello,

I have a multi-page post script file (that was generated by gnuplot, if that
matters) and I'm interested in using convert to turn only certain pages into
png's.  The following command will convert the 10th page of the postscript
file:

convert "multipage.ps[9]" page10.png

On two different machines I have access to this works great.  On a third
machine, page10.png is the first page from the postcript file no matter what
number I put in the square brackets.  Any ideas what may be failing on the
3rd machine?  

The specifics of the two machines that work properly:

ImageMagick 6.2.8, CentOS 5.3, x86_64
ImageMagick 6.3.2, SUSE Linux Enterprise Server 10, ia64

And the machine that will only grab the first page:

ImageMagick 6.4.5, Ubuntu 9.04, x86_64


Thanks,
Darby