Hi again!
Just wondering - have you tested the plugin against Paypal's Enhanced Checkout instead of the Classic Checkout?
I (randomly) have different browsers going to different types of checkouts (some people in Firefox will land up on the Enhanced Checkout, and some will land up on the Classic), however when I'm in the Enhanced Checkout, the cart doesn't clear after the transaction is finished.
It works totally fine on the Classic Checkout though. Weird?