1st page of PDF problem - gives an animated GIF!

Hi,

I'm using magick to create an image of the first page of a PDF  
document. I use the following command:

convert -resize 150x -crop 150x150! -gravity center -strip -colors  
128 -resample 72x +repage 'file.pdf'[0] 'file.gif'

This has worked perfectly for me apart from 1 exception. For one PDF,  
I end up with an animated gif containing two frames. So, it seems to  
be ignoring the [0] part?

In the animated GIF - the first frame is correct, but the second is  
the part of the image that did not make it inside the crop region  
specified.

Any ideas?

Many Thanks,

~ Mark