Bank Code field being populated with strange characters

[aingham]

We had a problem whereby none of the enabled payment methods were being displayed on the 'Payment' tab of the onepage checkout. We identified that there were invalid characters in the HTML that was being loaded via Ajax, causing none of the content to be loaded.

When I changed form.phtml to allow display of strange characters (getAccountBLZ()); ?>) we see the following:

At a guess this is maybe caused by the following code in Form.php?

Any help on this would be much appreciated.