Hi,
I'd like to contribute a bug report, I'm not sure if this is the place to do it, but here it goes...
This has been bugging me for months, but only now did I understand exactly how to reproduce it!
I'm running Fences 1.01.143, free version, on a 64-bit Windows Vista SP2.
I use a double monitor setup (with all my icons on the main monitor) and - this might be important - my Windows Explorer is configured to open icons with a single-click, and to show a check-box on the icons to select them.
I use Fences quick-hide, but the icons I refer to in this post are not inside the quick-hide list, i.e., they are always showing.
I noticed that occasionally certain icons (one or two at a time) would appear outside their fences after a return from a locked screen (or an hibernation). They appear to be moved to random places on the Desktop. Then I place them back where they belong, until they "decide" to do their trick again...
Finally I realized that the icons being moved where the ones I had clicked during that session. When clicking them, they get selected on the Desktop (well, inside a fence), and that seems to cause Fences to move them when the computer returns from a screen lock.
I then confirmed that this happens not because of actually opening the icons, but simply because of the fact that they are selected.
Steps to reproduce:
1. Select an icon inside a fence
2. Without de-selecting it, tell Windows to lock the screen
3. Come back to the Desktop by typing your password and see the icon getting moved outside the fence.
Does this help? It is very annoying... but Fences must be a great program because I keep using it regardless! 
Thanks!