Ok. I replicated the effect here:
You have to copy the exact images, properties and values from the theme into Aero > Top > PlacesList and Aero > Top > LogOff.
You also have to copy the exact values from the theme into the DefaultPaneSize:Rect of Basic > Places List and LogOff.
Then you will have the correct overflow effect.
If you don't understand then upload your msstyles and PM me a link and I'll do it for you and send the finished msstyles back to you