BUG #7644: Missing implicit types of Result and failing type-conversion

The following bug has been logged on the website:

Bug reference:      7644
Logged by:          Bernhard Reutner-Fischer
Email address:      rep.dot.nop@gmail.com
PostgreSQL version: 9.1.6
Operating system:   debian
Description:        =


Hi,

According to
http://www.postgresql.org/docs/9.1/static/typeconv-union-case.html

i think that these 2 (separate?) issues are bugs(?)
1)
select distinct on (bug) bug
from (
        select * from (select 'string one' AS bug from generate_series(0,1))
s1
        UNION
        select * from (select 'string two' bug from generate_series(0,0))
s2
     ) x
;
ERROR:  could not determine which collation to use for string comparison
HINT:  Use the COLLATE clause to set the collation explicitly.

When casting the return value of the union to :text _explicitly_ it works as
expected:
select distinct on (bug) bug
from (
        select * from (select 'string one'::text AS bug from
generate_series(0,1)) s1
        UNION
        select * from (select 'string two' bug from generate_series(0,0))
s2
     ) x
;
    bug     =

------------
 string one
 string two
(2 rows)

2)
select distinct on (bug) bug
from (
        select * from (select 'string one' AS bug from generate_series(0,1))
s1
        UNION
        select * from (select 'string two' bug) s2
     ) x
;
ERROR:  failed to find conversion function from unknown to text

In this case, however, using a "Result" fails to implicitly typecast to
:text, i.e. casting the return value of the first return value of the union
to :text explicitly does _not_ work:

select distinct on (bug) bug
from (
        select * from (select 'string one'::text AS bug from
generate_series(0,1)) s1
        UNION
        select * from (select 'string two' bug ) s2                        =


     ) x
;
ERROR:  failed to find conversion function from unknown to text

What am i missing or doing wrong?
thanks and cheers,