Hi.

It may happen to others. If you got here, you will understand the issue. As this site is RTL, the problem was having the right part of the styled button even though it got background: none. This is due to parenting div. Anyway, here is the code that helped us.

// Fixes back and cancel buttons in the checkout pages which got the right part of the Button Style module. (Tzvika)
jQuery(function() {
	jQuery("#commerce-checkout-form-shipping .form-button-wrapper:has('#edit-back')").css('background','none');
	jQuery("#commerce-checkout-form-review .form-button-wrapper:has('#edit-back')").css('background','none');
	jQuery("#commerce-checkout-form-checkout .form-button-wrapper:has('#edit-cancel')").css('background','none');
});

I open it as a feature request, as this might get to the code (or not, depending on maintainer).