Valid query fails with ERROR X0A00: The select list mentions column 'A' twice...

The following query is valid but fails with 10.2

ij> create table bug280
(
a int,
b int
);
0 rows inserted/updated/deleted
ij> insert into bug280( a, b )
values ( 1, 1 ), ( 1, 2 ), ( 1, 3 ), ( 2, 1 ), ( 2, 2 );
5 rows inserted/updated/deleted
ij> select a+1 as a, a+1 as a from bug280 group by a;
ERROR X0A00: The select list mentions column 'A' twice. This is not allowed in queries with GROUP BY or HAVING clauses. Try aliasing one of the conflicting columns to a unique name.