zenity 3.8 --list outputs first answer twice separated by a pipe

Selecting the first item from

$ zenity --list --column "Item" Apples Oranges Pears Toothpaste

now returns

`Apples|Apples`

while in 3.6 it returned just `Apples`.

Similarly,

$ zenity --list --column "id" --column "Item" 1 Apples 2 Oranges 3 Pears 4
Toothpaste

now returns `1|1` instead of `1`.

This messes up a lot of scripts expecting the old behaviour.

(originally reported at https://bugzilla.gnome.org/show_bug.cgi?id=711251 but the bug doesn't appear in git master, nor apparantly in 3.8 as installed by the developer)