bug with distinct?

I dont' know if this a bug or I am just out of my mind, but since it
works with other RDBMS's I decided to ask, so here it goes:

I am trying to do the following:

SELECT distinct 'mod_type' ,currval('mytable_idmytable_seq') from
mytable;

and I get the message:

ERROR: Unable to identify an ordering operator '<' for type 'unknown'
Use an explicit ordering operator or modify the query

Thinking it could be because of the currval I tried the following:

SELECT distinct 'mod_type', idmytable from mytable

getting the same result.

Am I doing something wrong? Is there a way to do this? Is this a bug?

Thanx

P.S. If someone is wondering what the heck I am trying to do.... I
pretend to insert into a log table, the mod_type for 'mytable' (in this
case insert) and the new inserted row for 'mytable'.

Cheers