Problem with fixed-length column query from Oracle

Hi,
I am quering Oracle DB from SQL server as below:

SELECT sysdate,a
FROM OPENQUERY([Myserver.xp.COM],'
select sysdate,to_char(''muntasir'') as a from dual')

shows:
Server: Msg 7347, Level 16, State 1, Line 1
OLE DB provider 'MSDAORA' returned an unexpected data length for the fixed-length column '[MSDAORA].A'. The expected data length is 32, while the returned data length is 8.
OLE DB error trace [Non-interface error:  Unexpected data length returned for the column:  ProviderName='MSDAORA', TableName='[MSDAORA]', ColumnName='A', ExpectedLength='32', ReturnedLength='8'].

But ok with

SELECT sysdate,'Muntasir' as a
FROM OPENQUERY(Myserver.xp.COM],'
select sysdate  from dual')

What is the problem? Can any one please explain or help to solve it?
Thanks in  advance