Black filled shapes have a thin white line on a dark background that shows in final video export.

I'm a new user, but after finding a bug in the rate stretch tool in small clips (forced zooming), I have another issue that no one at the help desk can solve. Here is how to recreate the problem I find everytime I edit footage that has a bright object with a dark background. 

1: Film a total black room (i.e. keep lens cap on perhaps).
2: Insert footage into timeline.
3. Select the rectangle tool and cover part of footage (as you have to do with filming errors or background inconsistencies).
4. Fill the shape black.
5. Exclaim: "Why is that shape faintly outlined!!" 

The black shapes have a very fine shape surrounding it that you cannot remove, and worse still when you export it, the outline is slightly visible which shows up all your filming cover errors. This does not happen in Premiere Elements v10.

Why is this? I have tried all manner of methods to remove it. Attached screen grab of problem, but I upped contrast so you can see fine lines on any resolution screen at your end. There is no stroke or shadow on the shapes. 

Is this another bug or is there an easy work around?