begin/end/abort work for sequences?

I assumed that wrapping a call to nextval() in a transaction would allow
me to roll back the update of the sequence.  But when I do the following:

  begin;
  select nextval('po_seq');
  abort;

The sequence po_seq is advancing to the next value even though the
transaction was aborted.  If I put other things like updates, inserts, etc.
inside the transaction, they seem to be rolled back OK, but not the
update of the sequence.

Am I doing something wrong?

 ----------------------------------------------------
 Kyle Bateman       President, Action Target Inc.
 "Viva Yo!"         kyle@actarg.com (801)377-8033x101
 ----------------------------------------------------