Why is my photo showing as if they are on a low opacity over a transparent background?

Help,

I'm stymied.  I'm using PS Beta.  I made a copy of a layer CTRL+J at 100% opacity yet it shows as if it is a low opacity layer over a blank transparent layer, i.e. showing a diamond grid.  If I flatten it the "artifacts" disappear.  If I put a black layer under it the "artifacts" disappear which is a bit nuts since the top layer is 100% opaque.  

Any ideas why & how to combat / correct this glitch?

If you zoom the screenshot you can see the pattern and the other with the black layer underneath with no pattern.

Thanks!