Strange SQL statement

 I am in EBS R12 DB, I get a sql from an SR which is oracle support reply to me.

The sql is like below

select * from gl_code_combinations_kfv where code_combination_id in (select code_combination_id from mtl_system_items);

This sql statement can be ran without any error message, many rows are returned.

BUT, the point is in the subquery. Actually, there is no code_combination_id column in mtl_system_items table!!

If I just execute "select code_combination_id from mtl_system_items", I will get error message "ORA-00904: "CODE_COMBINATION_ID": invalid identifier"