Layer effects drop shadow spread introduces artifacts

I added a drop shadow to a single layer with a transparent background and get incorrect results.  When increasing the spread slider past a certain point it creates random drop shadows for parts of the layer.  Lowering the spread to zero or very low value eliminates the error.   This happens in the beta release and the production release.    Beta 27.2 m3292.  also production 27.1.0

See attached psd where I have circled the random shadow.  The original layer is just the black flower.  The screenshots show the settings and results.