Syntax question - compound value comparisons

I can do this:

SELECT * FROM library_items WHERE (li_lib, li_item) = (11080,123063);
 li_lib | li_item
--------+---------
  11080 |  123063

But not this:

SELECT * FROM library_items WHERE (li_lib, li_item) IN ( (11080,123063),
(11081, 122250) );
ERROR:  syntax error at or near "11080" at character 59

Is this just a parser weakness (in which case, can I ask someone in core for a
TODO - tia) or is there some subtle reason why it isn't supposed to work.

--
  Richard Huxton
  Archonet Ltd