Checkout process dies a horrible death if a commerce_fieldgroup_pane has been removed from the checkout form.

We are using fieldgroup panes to expose a bunch of fields on the checkout orm to collect donor comments amongst other things. However, we only want this checkout pane to be present if a certain 'donation' product type is in the cart. So, in hook_form_FORMID_alter we unset the entire fieldgroup unset($form['commerce_fieldgroup_pane__group_cw_fundraising_comments|commerce_order|commerce_order|form']);

However, this causes the checkout process to die with a wsod as the submit handler tries to call field_attach_submit() passing in $form[$checkout_pane['pane_id']] which is expected to be an array- in our case it's not set as we unset it.