Obscure behavior of ORDER BY

Hi everyone!

I recently noticed obscure behavior of ORDER BY. Consider this example:

select email from
(
select '@'::text as email
union all
select '.'::text as email
) a
order by email;

The result is: email
------- . @
(2 rows)

This is all normal - I expect, that dot is smaller than ampersand. But 
if I add anything after dot, the order is reversed:

select email from
(
select '@'::text as email
union all
select '.m'::text as email
) a
order by email

The result is: email
------- @ .m
(2 rows)

Why is this happening? As dot is smaller than ampersand, anything after 
dot shouldn't matter.

I'm using PostgreSQL 8.4.7 on 32-bit Debian.

Thanks in advance,  Tambet