Window Function Expressions Wrong Results

create table t(a decimal(35,10), b int);

insert into t(a,b) values(1,1);

insert into t(a,b) values(2,1);

insert into t(a,b) values(0,1);

select * from t;

a	b

1.0000000000	1

2.0000000000	1

0.0000000000	1

select sum(t.a) over (partition by t.b) as s1, sum(t.a) over (partition by t.b) + 1 as s2

from t;

s1	s2

3.0000000000	1.0000000000

3.0000000000	1.0000000000

3.0000000000	1.0000000000