union involving double column with a map join subquery will fail or give wrong results

The following query fails:
select * from (select cast(a.key as bigint) as key from src a join src b on a.key = b.key union all select cast(key as double) as key from src)a

The following query gives wrong results:
select * from (select cast(a.key as bigint) as key, cast(b.key as double) as value from src a join src b on a.key = b.key union all select cast(key as double) as key, cast(key as string) as value from src)a

But the following query runs fine:
select * from (select cast(a.key as bigint) as key from src a union all select cast(key as double) as key from src)a