Floating Backgrounds in KDe 4.4.4

Hello everyone.
I just configured my kde 4.4.4 to have

  • 6 virtual desktops
  • different background image for each virtual desktop
  • 1 common dashboard for all the 6 virtual desktops

The problem is that I can to scroll the backgrounds (not on purpose) because somehow backgrounds are not locked and can be moved around.

Thus I need some help with that.

Could you please help to lock the backgrounds at their positions?

I would like to thank u in advance for your help
Best Regards