I have an unhacked, unmodified version of classifieds 2.42 and I have the same exact problem. I received the following email:
I did NOT hit the "back" button at any point in the transaction, and PayPal returned me appropriately to the Classifieds program where the ad displayed properly.
table "pp_payments" updated correctly:
id = 4
ad_id = 7
ad_amount = 3.00
ad_key = f872db3d903a1dd298aa58f1c7dc9086
If "ad_amount" $3.00 is there in the database, why isn't it ending up on our notification emails?