I'm on version 3.5.2 (530) Professional Edition, but thank god it is a bug because it has been driving me insane for weeks now! It's not any particular scene it's every scene I duplicate or new layout or eve cut and paste from one scene to another.
Might it be because I got it from Mac App Store with upgrade to pro via in-app-purchase? I'll try deleting and reinstalling again
(retyped due to previous post disappearing from thread!)