Yes, the problem is Talend currently does not handle CLOBs and therefor they will be processed as VARCHAR fields. A VARCHAR2 field in Oracle is limited to 4000 characters.
The only way at the moment is a user component from Talend Exchange tOracleTableTransfer. This component copies the data from one table to another without inspecting the columns, it use always the Objects and this could work.
I am working on CLOB and BLOB support for Talend.