ALTER TABLE ADD column with DEFAULT value and Virtual Private Database

I recently came over a real strange behaviour with ALTER TABLE ADD column with DEFAULT value on one of my customers. They are using a Software Product based on WebLogic and Oracle Database, from time to time we receive some new version of this Software Product which includes Database related changes, e.g. add new tables, add columns to an existing table and so on. Within the latest Software Update, we could observe that the overall update process for the Database related part was increasing to around 12 hours !!!! Before it was quite shorter. Mainly...