Does a 100% coupon in MarketPress just apply to product cost and NOT shipping?

Hi

Have created a coupon worth '100%'. At checkout, it seems to apply only to product cost. This causes an error (see image upload) during checkout.

Maybe I'm configuring something wrong? Or does a 100% discount only apply to the product cost? If so, then its still not letting the checkout process complete.

I can provide a coupon code for you guys to try - if you let me know how to get it to you.

Many thanks,

Martin