As we're looking to go to 12c, I've found myself paying more attention to this content so MOS note 1634495.1 grabbed my attention when it talked about receiving the following when trying to drop a tablespace in a 12c PDB:
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-65040: operation not allowed from within a pluggable database
This is especially interesting for me as the application on top of the database that we are migrating to 12c uses tablespaces as versioning, so we started out with VERSION as the initial tablespace name and the next release was in a tablespace named VERSION2, etc. Well, what happens now when we migrate the database to 12c and our initial tablespace can no longer be removed? This note tells you why it is an issue, how you resolve it, and will be a key reference document I'm sure by our team down the road.