It seems that GF+CPT can't currently use URL (or shortcode) parameters to dynamically populate checkboxes or radio buttons if they are 'populated with taxonomy terms'.
(it will, however, populate the "other" box on radio buttons)
Here's an example of this (not) working on my site:
Any workarounds or future releases to make this tick?
Otherwise I'm simply LOVING this plugin! Adds a LOT of value to GF!