Version:            (using KDE 4.4.2)
OS:                Linux
Installed from:    Ubuntu Packages

In a computer with two monitors, one above the other, each monitor displays a plasma activity. The lower monitor is the primary one, the upper is the secondary.
Both activities are configured with slideshow wallpaper. The one on the upper monitor is configured to change the wallpaper every 30 seconds and the other is configured to change the wallpaper every hour.
The upper activity loads a wallpaper when the user logs in and changes it at the defined interval, as expected. The other one, however, does not load the wallpaper after login and never updates it.
It is possible, however, to change the wallpaper of the lower activity using the nextwallpaper plasma widget.