MarketPress Checkout Bug

When using the Paypal Express and Stripe payment gateways together, it doesn't allow me to proceed when clicking the "Continue Checkout >>" button. It appears that “input type=”submit” name=”mp_payment_submit” id=”mp_payment_confirm” value=”Continue Checkout »” is displayed twice in the form, which may be the source of the problem.

The problem exists on this page: https://www.ductworks.net/store/shopping-cart/checkout/, but you may have to add something to cart and go through the process to get to it.