Fast Export Data File Issue

Hi,
I am trying to export below column using Fastexport.
 
SELECT
CAST(COL1 as VARCHAR(4000))
from
TABLE;
 
When COL1 actual size exceeds 2559 chars , new record is getting added after that row having only one alphabetic char. 
Also, I observed one strage behaviour: usually when we try to export varchar data using FEXP, it gives some control chars which are nothing but VARCHAR data size (2 byte).  But in above case when VARCHAR record length is exceeding 2559 then that record is coming with no control char and one new records with one char is getting added after it in a file.