Table formulas: Cannot use column names on the left hand side

[Yu <yu_icq@gmx.at>]

Hello!

I tried today to use named columns for calculations. While this works
on the right hand side of the equation, names don't seem to work for
the left hand side -- which is a problem, because a change in column
arrangement, that isn't caused by org functions (e.g. manually
inserting a column with rectangle-copying) may cause an input column
to be overwritten accidentially (e.g. having a formula $4=$3*$2+$1 and
then manually inserting a column for line markers as described in
"Advanced Features").

Exactly this happened to me recently, forcing me to redo some by-hand
evaluation.

Here some examples to clarify the problem:

-----------------------------------------------------------------------------

Recalculation attempts done each with C-u C-c C-c in the table and
with C-c C-c in the formula line, and with C-u C-c *.

Works fine:
|   a |   b | a+b |
|-----+-----+-----|
| 1.0 | 1.0 | 2.0 |
| 1.5 | 0.5 | 2.0 |
| 0.5 | 0.0 | 0.5 |
#+TBLFM: $3=$1+$2;%.1f

Doesn't Work:
|   |   a |   b | a+b |
|---+-----+-----+-----|
|   | 1.0 | 1.0 |     |
|   | 1.5 | 0.5 |     |
|   | 0.5 | 0.0 |     |
| ! |   a |   b | ab  |
#+TBLFM: $ab=$a+$b

Doesn't Work:
|   |   a |   b | a+b |
|---+-----+-----+-----|
|   | 1.0 | 1.0 |     |
|   | 1.5 | 0.5 |     |
|   | 0.5 | 0.0 |     |
| ! |   a |   b | ab  |
#+TBLFM: $4=$a+$b

Even this doesn't work
|   |   a |   b | a+b |
|---+-----+-----+-----|
|   | 1.0 | 1.0 |     |
|   | 1.5 | 0.5 |     |
|   | 0.5 | 0.0 |     |
| ! |   a |   b | ab  |
#+TBLFM: $4=$2+$3

This works again; This is sort of consistent with the specification,
that "Unmarked lines are exempt from recalculation with C-u C-c *",
but there was no mention, that it affects other methods of causing
recalculation too in `(info "(org)")'.
|   |   a |   b | a+b |
|---+-----+-----+-----|
| * | 1.0 | 1.0 |  2. |
| * | 1.5 | 0.5 |  2. |
| * | 0.5 | 0.0 | 0.5 |
| ! |   a |   b |  ab |
#+TBLFM: $4=$2+$3

This again does NOT work.
|   |   a |   b | a+b |
|---+-----+-----+-----|
| * | 1.0 | 1.0 |     |
| * | 1.5 | 0.5 |     |
| * | 0.5 | 0.0 |     |
| ! |   a |   b | ab  |
#+TBLFM: $ab=$2+$3

Works again.
|   |   a |   b | a+b |
|---+-----+-----+-----|
| * | 1.0 | 1.0 |  2. |
| * | 1.5 | 0.5 |  2. |
| * | 0.5 | 0.0 | 0.5 |
| ! |   a |   b |  ab |
#+TBLFM: $4=$a+$b