Is this a BUG? my unicode-enabled database have some problem

hello!

I have created a unicode-enabled database by set the parameter 
_UNICODE to YES and the parameter DEFAULT_CODE to UNICODE.
Then,I input some data from sqlserver2000 to the database successful.
when I try to run some query statement,the error occur:

>Auto Commit: On, SQL Mode: Internal, Isolation Level: Committed
>General error;-2009 POS(1) Join columns too long.
>select em.STATUS AS status,    em.EMPLOYEE_ID AS employeeId,  
>em.EMPLOYEE_NAME AS employeeName,a.TIME_CONCUME as timeConcume,  
>a.END_DATE AS endDate,  p.PROJECT_TITLE_SHORTEN AS 
>projectName,ot.OPERATION_TYPE_TITLE AS operationType from  
>manhaur_temp AS a , empolyee as em, project as p,  operation_type as 
>ot,  operation as o where      em.EMPLOYEE_ID=a.EMPLOYEE_ID and  
>a.OPERATION_ID=o.EVENT_ID  and      
>o.OPERATION_TYPE_ID=ot.OPERATION_TYPE_ID and    
>o.EVENT_ID=p.PROJECT_ID

I tested several times,I found that if the statement include 3 tables 
it will run fine,more than 3 tables it will generate the General 
error;-2009 POS(1) Join columns too long.

Besides,I sometimes fall across the General error;-904 POS(1) Space 
for result tables exhausted,when I execute sql statement both at sql 
studio and according JDBC driver.

I have read the document carefully,but still confused.
At last,I also setup a non unicode-enabled database and try the same 
example,and it's run fine.
Is this a sapdb BUG?