Unknown character in a database datafile name

Hi Everyone,
I found that one of our datafile name seems to contain an unknown character.
Our database is 10.2.0.4 on HPUX.

I run this query and got the following output
  1* select file_id,'XXXX'||nvl(substr(file_name,1,90),'yyyy')||'XXXX' from dba_data_files
SQL> /
         1 XXXX/u01/oradata/clmdev/system01.dbfXXXX                                                                                                  
         2 XXXX/u01/oradata/clmdev/undotbs01.dbfXXXX                                                                                                 
         3 XXXX/u01/oradata/clmdev/sysaux.dbfXXXX                                                                                                    
         4 XXXX/u01/oradata/clmdev/RT_DATA_PROD_01.dbf                                                                                               
           XXXX                                                                                                                                      
                                                                                                                                                     
         5 XXXX/u01/oradata/clmdev/RT_INDX_PROD_01.dbfXXXX 
When I check the length of the filename,I got this:
SQL> select length(file_name) from dba_data_files where file_id in (4,5);