[cherie]

Update: this is for the default mobile checkout: Fast Lane Checkout. Switching mobile settings to One Page Checkout (check the box) appears to deal with this properly without needing a hack.

Here is a hack to ensure Payment Details is always expanded (also affects Gift Certificate payment method):

In skin/common_files/modules/Xcart_Mobile_Skin/customer/core.js:

Find:

function wlcOpener() {
    $('.panel.active .wlc-section').filter(':first').addClass('opened');

After add:

$('.collapsible-block').filter(':last').addClass('opened')