Bug in the org spreadsheet?

[Nikos Apostolakis <nikos.ap@gmail.com>]

Hello group,

it seems that algebraic entries on tables are not always parsed
correctly by org mode, or is it calc's fault?  For example in the
following table the the entry @2$4 should be -a^4 - a^2 b^2


| Term | Components | vac        | Contribution                  |
|------+------------+------------+-------------------------------|
| a a  |          2 | -a^2 - b^2 | -a^4 - b^2                    |
| a b  |          1 | 1          | a b                           |
| b a  |          1 | 1          | b a                           |
| b b  |          2 | -a^2 -b^2  | -(b^2 a^2) - b^2              |
|------+------------+------------+-------------------------------|
|      |            |            | 2 a b - a^4 - a^2 b^2 - 2 b^2 |
#+TBLFM: $4=$1*$3::@6$4=simplify(expand(vsum(@-I..@-II)))

I can get the spreadsheet to do what I mean by using parentheses as 
in the following table, but IMHO it shouldn't be necessary.

| Term | Components | vac          | Contribution                  |
|------+------------+--------------+-------------------------------|
| a a  |          2 | (-a^2 - b^2) | -(a^2 (b^2 + a^2))            |
| a b  |          1 | 1            | a b                           |
| b a  |          1 | 1            | b a                           |
| b b  |          2 | (-a^2 -b^2)  | -(b^2 (b^2 + a^2))            |
|------+------------+--------------+-------------------------------|
|      |            |              | 2 a b - a^4 - b^4 - 2 a^2 b^2 |
#+TBLFM: $4=$1*$3::@6$4=simplify(expand(vsum(@-I..@-II)))

,----[ M-x version ]
| GNU Emacs 23.0.60.1 (i486-pc-linux-gnu, GTK+ Version 2.12.9) of
| 2008-04-07 on elegiac, modified by Debian
`----

,----[ M-x org-version ]
| Org-mode version 5.23a
`----


Thanks, Nikos