The event "lightbox_open" is only triggered when the lightbox is initialized and not each time the lightbox is actually shown.
The description in the documentation (http://galleria.io/docs/api/events/#lightbox-open) states "Triggers every time the lightbox is opened.", which I take to mean that the event is triggered each time the lightbox is visible on the screen.
A clarification of the event, or a change to make the event trigger on show as well as on init would solve the issue. If the event is to only be triggered on init, then it would be nice with another event that would trigger on show.
Seems to be fixed in 1.3.2 (now fires on every image load)
Seems like it does. Closing.