Grid artifacts appear after having applied a live Gaussian Blur.
I first noticed the bug with v1.8,2 and hoped it would vanish with with the betas, V1.8.3 came out failrly quickly and, unforunately, the bug ist still there.
Let's start from the beginning. Applying a Gaussian Blur to an edge masked "Unsharp Mask" layer. Everything seems fine, but the grid is already there (and spoiling the unsharp mask)
Let's make the grid visible with a Curves adjustement
Moving the slider of the Gaussian Blur changes the grid
Tinus got a reaction from Chris B in Grid artifacts using live Gaussian Blur