Photoshop :: Using Dust And Scratches Filter In CS6?

Using the 64-bit extended CS6 version under Win 8/64.  Am I not using the filter correctly, or is this a limitation regarding its use?
 
I duplicate a layer and apply the filter.  I then add a white mask and invert it to get black.  I change the layer blending mode to either darken or lighten, depending on the requirements at hand.  I use the paint brush to remove the spotting and it works.  However, if I add a new layer and then go back to the Dust and Scratches layer, the paint brush further modify the layer.  I need to create a new layer and start all over again.
 
I am finding that if I convert the layer for smart filter use, I cannot use the paint brush.  The layer needs to be rasterized, again.