Sound switching is messy in slideshow projects

Ok, the summary of my problem as follows: when in a slideshow I change positions of individual photos (or groups of photos), then it changes the sound setting switching it on even if the sound checkbox is unticked. If I want my choice of having it off to take effect I have to quit iPhoto and then to open it again. Has someone encountered this misbehavior? Is this a bug and if not, how do I make it to act consistently?

I.S.

OS X version and hardware are as indicated at the bottom. iPhoto is v.9.4.3