it shud replace the contents by drop and recreate..

REPLACE

Replaces destination_table and its contents with the rows from query. If destination_table does not exist, COPY creates it. Otherwise, COPY drops the existing table and replaces it with a table containing the copied data.
Can you post result of below query

Select Object_Name, Object_Type From All_Objects Where Owner = 'USER1' And Object_Name = 'CASTING';

Abhay.