I am not a to sure what all the PayPal log files mean, but during my test purchase this morning, it did the usual loop where I logged into PP twice to get the order to go through. Of the multiple log files generated, one them contains the following:

Sep 23 2011 8:38 -- CURL response: VERIFIED

Sep 23 2011 8:38 -- IPN INFO (cl) - Confirmation/Validation response VERIFIED

Sep 23 2011 8:38 -- Breakpoint: 1 - Collected data from PayPal notification

Sep 23 2011 8:38 -- Breakpoint: 2 - Validated transaction components

Sep 23 2011 8:38 -- Breakpoint: 3 - Communication method verified

Sep 23 2011 8:38 -- Breakpoint: 4 - Details: txn_type=unknown ordersID = 0 IPN_id=0

Relevant data from POST:
txn_type = unknown
parent_txn_id = None
txn_id = 4VS2317816234613C

Sep 23 2011 8:38 -- Breakpoint: 5 - Transaction type (txn_type) = cart [parentLookup=unknown]

Sep 23 2011 8:38 -- Breakpoint: 5 - midstream checkpoint

Sep 23 2011 8:38 -- Breakpoint: 5 - Record does not need to be processed since it is not new and is not an update. See earlier notices. Processing aborted.
Not sure what is causing the Processing aborted in Breakpoint 5, but then I am not familiar with these files. Help appreciated.