It isn't not a bug and its not random. When you make a purchase at Autozone your transaction may be originated by Point of Sale (POS) identifier as "Autozone Store17 XXX". Your Starbucks transactions may have been identified as "Starbucks Store XXX". If you login to your web banks website to check your transactions you will notice it. Sometimes POS are different even within the store, i.e. each cash register will have its unique identifier.
My Money analyzes the strings and assigns each part of the string statistical importance, in this case "Store XXX" would be deemed more important than Starbucks and so both transactions would be brought to Autozone.
This matching could be adjusted or completely switched off through preferences, data matching algorithm is explained on wiki at see
http://wiki.mthbuilt.com/Data_Matching_AlgorythmThanks