Assignment of multiple navigation keybindings does not work

Using gsettings/dconf on the command-line it should, in principle, be possible to assign multiple keybindings to each action in the "windows" and "navigation" groups, since the keys in org.gnome.desktop.wm.keybindings are lists.

For example:
Action:
In a terminal enter:
gsettings set org.gnome.desktop.wm.keybindings close "['Pause', '<Alt>F4']"

Expected result:
Pressing either Pause or Alt-F4 results in the current window being closed.

Actual result:
Pressing Pause (i.e. the first keybinding in the list) closes the current window but Alt-F4 has no effect.

Present in Ubuntu 15.04.

(This bug is not very important, since the graphical "System settings > keyboard > Shortcuts" permits only the definition of one keybinding per action. However, the desired functionality (allowing multiple keybindings) is more logical and should work according to the wiki page:
https://wiki.ubuntu.com/Keybindings
(section org.gnome.desktop.wm.keybindings).
Also, in GNOME-shell, the definition of multiple keybindings via gsettings does work.)