GUI AnchorLayout broken when using ScrollArea

[DragonMoffon]

While trying to right align and left aligned different elements in a scroll area the UIAnchorLayout caused all of the UI to disappear. To test I made this small minimal snippet, and discovered that mixing UIBoxLayout and UIAnchorLayout led to the UIAnchorLayout children to draw over the UIBoxLayout.

from arcade import Window, gui
from arcade.gui import experimental


class TestWindow(Window):
    def __init__(self):
        super().__init__()
        self.manager = gui.UIManager()
        self.manager.enable()

        self.entry_box_1 = gui.UIBoxLayout(
            vertical=False,
            width=self.width,
            height=150,
            space_between=15,
            children=(gui.UIDummy() for _ in range(5)),
        )
        self.entry_box_2 = gui.UIAnchorLayout(
            width=self.width, height=150, children=(gui.UIDummy())
        )
        self.entry_box_2.add(gui.UIDummy(), anchor_x="left")

        self.scroll_box = gui.UIBoxLayout(
            width=self.width,
            height=4 * self.height,
            vertical=True,
            children=(
                self.entry_box_1,
                self.entry_box_2,
            ),
        )
        self.scroll_area = experimental.UIScrollArea(
            x=0,
            y=0,
            width=self.width,
            height=self.height,
            canvas_size=(self.width, 4 * self.height),
            children=(self.scroll_box,),
        )
        self.manager.add(self.scroll_area)

    def on_draw(self):
        self.clear()
        self.manager.draw()

    def on_key_press(self, symbol: int, modifiers: int):
        self.manager.debug()


win = TestWindow()
win.run()

Result:

Expected: