Bug: Org column view, property edit bug [7.8.11]

[Teemu Likonen <tlikonen@iki.fi>]

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Org's column view has "e" key for editing fields such as property
values. Properties are messed up if user tries to clear the property's
value with "e". See the following example.

Start "emacs -Q" and load this org file:

    #+COLUMNS: %9ITEM %5foo
    * heading
    :PROPERTIES:
    :foo: value
    :END:

Turn on the column view with "C-c C-x C-c". The buffer should look like
this:

    ITEM______|_foo___|_
    #+COLUMNS: %9ITEM %5foo
    * heading | value |
    :PROPERTIES:
    :foo: value
    :END:

Now move the point to the "value" column and edit it with "e". Clear all
the text from the minibuffer prompt and press enter. The buffer looks
like this:

    ITEM______|_foo___|_
    #+COLUMNS: %9ITEM %5foo
    * heading |       |
    :PROPERTIES:
    :foo: 
    :END:

Don't move the point. Press "e" again to edit the same value again.
Insert "xxx" to the minibuffer prompt. The buffer looks like this:

    ITEM______|_foo___|_
    #+COLUMNS: %9ITEM %5foo
    * heading |       |
    :PROPERTIES:
    :foo: 
    :foo: xxx
    :END:

See, there are now two "foo" properties: one with empty value and one
with the value "xxx". The column view will always show the empty value
but the edit command "e" will edit the latter value (currently "xxx").

I think the last "e" command in my example shouldn't create new "foo"
property line; it should edit the empty "foo" instead.


Emacs  : GNU Emacs 24.2.3 (x86_64-unknown-linux-gnu, GTK+ Version 2.20.1)
 of 2012-10-14 on mithlond
Package: Org-mode version 7.8.11