It sounds like you may be using the "PayPal Cart" version of button codes we make available for merchants who may have a very specific need to use PayPal's shopping cart system instead of using the standard E-junkie cart. Note this is unrelated to accepting PayPal checkout payments; you do not need to use our "PayPal Cart" button codes merely to accept payments via PayPal.
The problem you described recently cropped up due to a change in the way PayPal's cart system works, and we are working on a solution. We recommend using the standard E-junkie cart button codes, which will show buyers a PayPal checkout option in the E-junkie cart and also provide full support for our other cart-based features.
