I just stumbled over the Oracle 10/11 recycle bin functionality. It seems that when creating databases with the Oracle DBCA (Database Configuration Assistant), this feature is by default turned on. With this functionality, it is possible to recover dropped tables from the recycle bin.
This feature is not usefull when using this database for IdM, as with every initial load / update job, temporary tables are dropped. So at the end, the databse will grow up with each of this jobs running.
In order to turn of, use following commands: