'Order By' Clause Work Incorrect

when i try the following SQL batch, I get a result-set which is not order by
datetime column 'out_date',but if I delete clause INTO #fifo_temp, I get a correct result with correct order.

who can help me?thanks in advance
...
select tag,stuff_id,stuff_name,cast(out_id as char(10)) as out_id,out_number,out_date,out_qty,remark
INTO #fifo_temp from ##stuff_fifo UNION
select tag,stuff_id,stuff_name,out_id,null,out_date,quant ity,remark
from acc_cost.dbo.stuff_out where tag='A' and left(out_id,3) in ('XSA','TAP')
ORDER BY out_date

DROP TABLE ##stuff_fifo
select * from #fifo_temp

the following can get a correct result:

select tag,stuff_id,stuff_name,cast(out_id as char(10)) as out_id,out_number,out_date,out_qty,remark
from ##stuff_fifo UNION
select tag,stuff_id,stuff_name,out_id,null,out_date,quant ity,remark
from acc_cost.dbo.stuff_out where tag='A' and left(out_id,3) in ('XSA','TAP')
ORDER BY out_date