Gicon schema does not load scalable icons for toolbar actions

I'm trying to use system icons on a Toolbar using the gicon schema for iconSource.

This doesn't seem to work for scalable icons (i.e. the .svg ones):

                Action {
                    text: i18n.tr("Settings")
                    iconSource: "image://gicon/settings"
                    onTriggered: pageStack.push(pageSettings)
                }

Expected:

  * The toolbar action shows the /usr/share/icons/ubuntu-mobile/actions/scalable/settings.svg icon installed on my system

Actual result:

  * The toolbar action shows no icon at all