Can you explain why is this not correct?

SET DATEFIRST 1;

WITH SampleData (PERSON, [DATE], [HOURS], [DOW]) AS

(

SELECT 1234,'03/31/2014',8,'Monday'

UNION ALL SELECT 1234,'04/01/2014',8,'Tuesday'

UNION ALL SELECT 1234,'04/02/2014',8,'Wednesday'

UNION ALL SELECT 1234,'04/03/2014',8,'Thursday'

UNION ALL SELECT 1234,'04/04/2014',12,'Friday'

UNION ALL SELECT 1234,'04/06/2014',1,'Sunday'

UNION ALL SELECT 1234,'04/07/2014',9,'Monday'

UNION ALL SELECT 1234,'04/08/2014',8,'Tuesday'

UNION ALL SELECT 1234,'04/09/2014',8,'Wednesday'

UNION ALL SELECT 1234,'04/10/2014',8,'Thursday'

UNION ALL SELECT 1234,'04/11/2014',8,'Friday'

UNION ALL SELECT 1234,'04/12/2014',2,'Saturday'

UNION ALL SELECT 1234,'04/14/2014',9,'Monday'

UNION ALL SELECT 1234,'04/15/2014',9,'Tuesday'

UNION ALL SELECT 1234,'04/16/2014',9,'Wednesday'

UNION ALL SELECT 1234,'04/17/2014',8,'Thursday'

UNION ALL SELECT 1234,'04/18/2014',6,'Friday'

)

SELECT PERSON

,MIN(DATE) DATE

,SUM(CASE WHEN DATEPART(dw, DATE) <= 5

THEN CASE WHEN HOURS > 8

THEN 8

ELSE HOURS

END

END) AS REG_HOURS

,SUM(CASE WHEN DATEPART(dw, DATE) <= 5

THEN CASE WHEN HOURS > 8

THEN HOURS - 8

ELSE 0

END

END) AS DAILY_OT

,CASE WHEN SUM(HOURS) > 40

THEN SUM(HOURS) - 40

ELSE 0 END AS WEEKLY_OT

,SUM(HOURS) Real_Hours

FROM SampleData

GROUP BY PERSON

,DATEPART(WK, DATE);