BUG #5018: Window function alias

The following bug has been logged online:

Bug reference:      5018
Logged by:          Marko Tiikkaja
Email address:      marko.tiikkaja@cs.helsinki.fi
PostgreSQL version: 8.4.0
Operating system:   Linux
Description:        Window function alias
Details:

I came across this:

=> SELECT lead(foo) OVER(ORDER BY foo) AS foo FROM (VALUES(0)) bar(foo);
ERROR:  window functions not allowed in window definition

Changing the *column alias* to something else gives the expected answer. Is
this really the desired behaviour?