gtk_combo_box_entry_set_text_column: assertion `text_column >= 0' failed

[Luca <elvez84 gmail com>]

Hi, in my application I need to call twice
ComboBoxEntry::set_text_column, but the second time I call it, gtk
complains with the following assertion message:

> gtk_combo_box_entry_set_text_column: assertion `entry_box->priv->text_column == -1' failed

So I tried setting to -1 the column before calling again
set_text_column with a "valid" tree model column, but this cause the
assertion message I put in my subject, which I find strange given the
GTK+ documentation clearly states:

> The "text-column" property  "text-column"          gint                  : Read / Write
>
> A column in the data source model to get the strings from.
>
> Allowed values: >= -1
>
> Default value: -1
>
> Source: http://www.gtk.org/api/2.6/gtk/GtkComboBoxEntry.html#id3279961

I understand what I'm trying to do might not be the correct way to use
combo boxes, but being able to call more than once set_text_column
will keep my code much simpler.

Thanks for any help,

Luca