Is there any explaination from an NLS expert for this?

database was created nls_length_semantics = char  
instance is nls_length_semantics = char
 
session is nls_length_semantics = byte
 
 
this has cause some columns to revert back to byte ..
 
SQL> select  * from nls_database_parameters where parameter='NLS_LENGTH_SEMANTICS' 
PARAMETER
------------------------------
VALUE
--------------------------------------------------------------------------------
NLS_LENGTH_SEMANTICS
CHAR
 1* select  * from nls_database_parameters where parameter='NLS_LENGTH_SEMANTICS' 
 
 
PARAMETER
------------------------------
VALUE
--------------------------------------------------------------------------------
NLS_LENGTH_SEMANTICS
CHAR
 
 
SQL>  select  * from nls_session_parameters where parameter='NLS_LENGTH_SEMANTICS'    
PARAMETER
--------------------------------------------------------------------------------
VALUE
--------------------------------------------------------------------------------
NLS_LENGTH_SEMANTICS
BYTE