I mentioned this in a general forum post earlier and since others have confirmed the same I am putting it in the bugs forum.
Membership upgrades can be put into the cart and member can checkout (go to the processor and make payment) but Dolphin 7.1 site does not upgrade membership or clear cart. Sometimes the pending membership upgrade appears in the pending orders section of the admin area payment module, sometimes it does not. If a pending order does appear in the pending orders area and you use the manual process button, the pending order disappears, it does not move to the processed orders area or upgrade the membership or clear the cart.
A look directly in the site database shows the transaction in the pending transactions table (bx_pmt_transactions_pending). However the table shows a "successfully updated" message in the "error" column of the table.
I have tested with the stock Paypal IPN, 2checkout, and custom CCBill and Zombaio processors. All show the same behavior.