I can't move photos to events by flagging them

The simplest way to move photos from one event to another is by flagging them, then going to the target event, selecting it, and then going to the menu item 'Move flagged photos to selected event'

But when I do that, nothing at all happens. The photos remain flagged, but don't move.

I have found other ways to move them, but this would be the best, and I am wondering why it doesn't work