I have disabled all plugins but yours and I have updated and activated the default Theme Twenty Fifteen. It still has the same issue.
I have tried with the official Woocommerce cart of my site: http://www.edinventa.com/cart/?fill_cart=2841&apply_coupon=descuentosm
Exactly the same problem. So it’s not incompatibility with Onepage Checkout. So if default theme is used and no other plugins installed. What the hell can be? xD
I also trying disabling all plugins but Woocommerce, onepage checkout and yours. I also have changed the theme to a default one and updated it (Twenty Fifteen).
It has the same problem, if we visit
then remove the product
then going back to http://www.edinventa.com/checkout/, the product is not added anymore in Chrome or Firefox (it’s added in Safari.