I’m also having this same issue.
I have tried creating a pricing option for each (px, in, cm) and attempting to see if it would change once in the cart, but it doesn’t. Each time it shows ‘in’ which is not allowing my customers to download. (Which is all I offer)
Image Store Version: 3.2.4
WP Version: 3.5.1
Link to store on my site: http://www.attazack.com/photos/
Please help! You have the best Image Store plugin for what I need, and it’s not working!