Window aggregates invalid error/error messages in some cases

select count( * ) over () from emp group by deptno 
AssertionError: star should have been expanded.

SELECT sum(empno), max(empno) OVER (order by deptno) 
FROM emp 
GROUP BY empno 
gives error: Expression 'DEPTNO' is not being grouped

SELECT sum(empno), max(empno) OVER w 
FROM emp 
GROUP BY empno 
WINDOW w as (order by deptno)
gives no error:

select cume_dist() over w , rank() 
from emp 
window w as (partition by deptno order by deptno)
Assertion Error: Expression 'DEPTNO' is not being grouped
instead of 
Assertion Error: OVER clause is necessary for window functions