[Fixed] Eraser

Hi
My eraser is behaving strangely; it erases the lines but leaves a gray mark all the way around. Any explanation for that?
Just can't use Black Ink unless I don't use the eraser!
Thanks.
PS
I forgot to explain that this just hapens when I open a already saved file.
The original image, looks normal, just after saving and reopening I can see the eraser stains.
My eraser is behaving strangely; it erases the lines but leaves a gray mark all the way around. Any explanation for that?
Just can't use Black Ink unless I don't use the eraser!
Thanks.
PS
I forgot to explain that this just hapens when I open a already saved file.
The original image, looks normal, just after saving and reopening I can see the eraser stains.