BUG #4829: nth_value does not allow window frame

The following bug has been logged online:

Bug reference:      4829
Logged by:          lily li
Email address:      lil@sybase.com
PostgreSQL version: 8.4.0-lb2-windo
Operating system:   window 2000
Description:        nth_value does not allow window frame
Details:

I type in query
select c1, c2, nth_value(c2, 2)over (partition by c1 order by c2 rows
between 1 preceding and 1 following) from tab1;

I got syntext error ' error near '1';

without window frame clause query returned correct results;

According to 2008:SQL nth_value and first_value support window frame
clause.

It looks like postgreSQl 8.4 does not allow window frame clause inside OVER
clause.

Is this the current limitatio? Or a bug.

Thank you.