can’t create wallpaper slideshow in fvwm-crystal

I’ve got my wallpaper placed into the right directory, but when I select ‘Random Wallpaper’ from the ‘Auto Wallpaper” submenu in ‘Preferences”, a wallpaper is randomly placed on the screen once and I still have to manually change the wallpaper every so often and I’m not given the opportunity to set an auto-change schedule. What’s the deal?