Creating transactions throws undefined index for payment details

Whenever I "Add payment" through the UI interface, I get this error notice: Notice: Undefined index: payment_details in commerce_payment_order_transaction_add_form_validate() (line 197 of ... payment/includes/commerce_payment.forms.inc).. I haven't been able to figure out how to resolve the issue on my own.

The same error gets logged to the database when a new order is created. The error there occurs on Notice: Undefined index: payment_details in commerce_payment_pane_checkout_form_submit() (line 161 of ... payment/includes/commerce_payment.checkout_pane.inc).

Any ideas?

Thanks,
Rocket