Roto Brush to Mask

I'm having a problem turning my Roto Brush into a Mask using "Auto-trace." Every time I delete the Roto brush after making a mask the background comes back in the image. It's showing the object is still masked, but the mask doesn't have any impact on the image.  There has to be a step that I am missing? 

I'm trying to take a still image and separate it into fore, middle and background so I can move them individually over a 10-second span. I don't want to just use Roto brush because I have to reRoto every few frames, even though it's a still image.  I'm open to suggestions if there is a better way of doing this.