BUG #8329: UPDATE x SET x.y = x.y + z does not work in PL/pgSQL

The following bug has been logged on the website:

Bug reference:      8329
Logged by:          Petr
Email address:      chmelarp@fit.vutbr.cz
PostgreSQL version: 9.2.4
Operating system:   Fedora x64
Description:

Hi there,
we have an issue - if I run a query from a console, it runs OK. When it is
run using EXECUTE in an PL/pgSQL function, it sets NULL. The simplest
version of the query is like this:
UPDATE x
SET x.y = x.y + z.
FROM (SELECT z) as Z
WHERE ... ;


If I don't use the "+" in the SET command, it works OK. The whle query is
quite complex, but OK in a console. If you need the query an tables..., mail
me, please. I can't make it public.