Landscape Layer painting does NOT paint Alpha or Splat Map over the bottom texture

As said the Paint tool for the editor doesn’t seem to be able to paint the alpha weight of the texture/splatmap…
This seem to be broken since previous versions of the Engine. Been trying some really simple intro tutorial and after working previously the Layer won’t let the aplha from the top texture overlap the bottom one…

If the feature is buggy that’s understandable, Not sure if I’ve done Something wrong.

Thanks