Label missing if group not present in first facet

[jkrumbiegel]

data((; x = 1:2, y = 1:2, z = ["A", "B"])) *
    mapping(:x, :y, layout = :z) * visual(Scatter, color = :red, label = "Both") +
    data((; x = [3], y = [3], z = ["A"])) *
    mapping(:x, :y, layout = :z) * visual(Scatter, color = :blue, label = "First") |> draw

But:

data((; x = 1:2, y = 1:2, z = ["A", "B"])) *
    mapping(:x, :y, layout = :z) * visual(Scatter, color = :red, label = "Both") +
    data((; x = [3], y = [3], z = ["B"])) *
    mapping(:x, :y, layout = :z) * visual(Scatter, color = :blue, label = "Second") |> draw