Using a background color for a view with some alpha (e.g. #99fe0038) and some elevation on API 21 reveals two circles: one for the view itself and another inside:
Elevation and background color are set via code:
view.setElevation(getResources().getDimensionPixelSize(R.dimen.fab_elevation_lollipop));
view.setBackgroundColor(Color.parseColor("#99fe0038"));
Without setting elevation or with using an opaque color everything looks like expected.
Is it an Android bug or have I missed something here?