SQL & PL/SQL :: Datapump Field Length

I have a problem to read in data from dmp file to target table.

I've created a dmp file using:

CREATE TABLE table_name
ORGANIZATION EXTERNAL
(TYPE oracle_datapump
DEFAULT DIRECTORY directory_name
LOCATION ('file_name.dmp')
) AS SELECT col1, col2, col3 from source_table;

[Code]...

The file created via db_link from target db to remote db and then the data are insterted into target db table target_table.

desc target_table
col1 varchar2(20)
col2 number
col3 number

There are no values longer than 20 characters in source table, but when I insert into target_table(col1, col2, col3) as select col1, col2 col3 from source_table; I get ORA-12899: value too large for column "target_table"."col1" (actual: 25, maximum: 20).

I gues it has something to do with how the oracle datapump stored the data in dmp file. When I select col1 from source_table where length(col1) > 20; I get two values which clearly are not longer than 20 characters.

Selected values are:

748473358           
693197674           

where the bug is hidden or any "normal" workaround?