order by is ambiguous

I could not find any discussion on this but imho this seems an erroneous
error occuring now in 7.3.4 (after upgrade from 7.2.3):

select  null::time, 'test'::varchar as time order by time;
ERROR:  ORDER BY 'time' is ambiguous

The solution is to name the time datatype e.g.

select  null::time as xyz, 'test'::varchar as time order by time;

Regards,
Alfred