this is what I'm doing:
convert input.png -fill white -resize 2480x3508^ out.png
and I get:
convert: invalid argument for option `2480x3508^': -resize.
Version: ImageMagick 6.2.8 06/11/08 Q16 http://www.imagemagick.org
The error doesn't present itself if the '^' at the end of the Geometry argument is removed.