Using a stock v1.5.1 install (localhost) running php 5.4.8 on Windows 7. Added the product New v1.2 -> Downloads -> Single Download to my cart, signed in and clicked the Checkout button. I was properly redirected to the checkout_payment page, but had two debug*.log files generated:

Code:
[19-Nov-2012 20:12:07 Europe/Berlin] PHP Warning:  Illegal string offset 'cost' in C:\xampp\htdocs\v1.5.1\includes\classes\order.php on line 355

[19-Nov-2012 20:12:07 Europe/Berlin] PHP Warning:  Illegal string offset 'title' in C:\xampp\htdocs\v1.5.1\includes\modules\pages\checkout_shipping\header_php.php on line 88
Code:
[19-Nov-2012 20:12:08 Europe/Berlin] PHP Warning:  Illegal string offset 'cost' in C:\xampp\htdocs\v1.5.1\includes\classes\order.php on line 355

[19-Nov-2012 20:12:08 Europe/Berlin] PHP Warning:  Illegal string offset 'id' in C:\xampp\htdocs\v1.5.1\includes\classes\shipping.php on line 32

[19-Nov-2012 20:12:08 Europe/Berlin] PHP Warning:  Illegal string offset 'id' in C:\xampp\htdocs\v1.5.1\includes\classes\shipping.php on line 32

[19-Nov-2012 20:12:08 Europe/Berlin] PHP Warning:  Illegal string offset 'id' in C:\xampp\htdocs\v1.5.1\includes\modules\order_total\ot_shipping.php on line 41

[19-Nov-2012 20:12:08 Europe/Berlin] PHP Warning:  Illegal string offset 'id' in C:\xampp\htdocs\v1.5.1\includes\modules\order_total\ot_shipping.php on line 41
In each case, the illegal offset is associated with an undefined array element. For example, line 355 of order.php contains:
Code:
                        'shipping_cost' => $_SESSION['shipping']['cost'],
I'm not quite sure how to proceed. Are these warnings indicative of something that might become errors in a future version of PHP?