Playing around with the beta and noticed a difference in how 3.7 and 4.0 handle the Silhouette Luma/Alpha blend mode. I has a source from a 3rd party app that I use as a mask with the Silhouette Luma or Silhouette Alpha Blend mode. In 3.7 it blocks the image below except where there is input from the program. In 4.0 it just layers it over with a ghost layer.
I'm rather ignorant in exactly what is happening here but the behavior is pretty different from 3.7 and 4.0