PS4 and PayPal Std doubling/triping my shipping charges

I was contacted by a customer today that they were placing an order and the shipping doubled/tripled when they went from the PS4 order confirmation to the Paypal STD payment page. I haven't changed anything within the system since I initially configured and rolled out the system so I am not sure what may have caused this issue.

I reviewed the settings on the PS4 Admin\Settings page for USPS shipping, which is the only shipping I provide for, and I did not see anything incorrect there. See attachment Admin - Shipping Settings ( I hid the USPS User ID before taking the screen shot)

Here is the sequence of events.
- Customer selected items they wanted to purchase and navigated to the PS4 Order Confirmation page where they reviewed their information and pressed the "Submit Order" button(see attachment WebAssist - Purchase Order Confirmation Page).
- Customer is tranferred over to the PayPal Standard page where the pricing, tax and shipping is still consistent with the prior WebAssist page. I fill in my credit card information and press the "Review and Continue" button (see attachment PayPal STD - Order Summary)
- An additional $10.70 for Express shipping is now being added on the PayPal Purchase page, even though shipping was previously calculated (see attachment PayPal Std - Order Summary with Zip entered).

On the webassist/plugins/shopping_cart/ipn.php p[age, change:

$_SESSION["WA_Store_Cart_USPS_Quote"] = isset($_POST["mc_handling"])?$_POST["mc_handling"]:"";

to:

$_SESSION["WA_Store_Cart_USPS_Quote"] = 0;