VSplit width seems incorrect with Button children

Given this code:

#!/usr/bin/env python

from prompt_toolkit import Application
from prompt_toolkit.key_binding import KeyBindings
from prompt_toolkit.layout.containers import HSplit, VSplit, Window
from prompt_toolkit.layout.controls import FormattedTextControl
from prompt_toolkit.layout.layout import Layout
from prompt_toolkit.widgets import Button, Frame

buttons = []
for text in ["Yes", "No", "Maybe", "So"]:
    button = Button(text)
    # button = Window(FormattedTextControl(f"< {text} >"), height=1)
    buttons.append(button)

ftc = FormattedTextControl("This is just some text.")

root_container = HSplit([
    Window(content=ftc, wrap_lines=True),
    Frame(VSplit(buttons, align=HorizontalAlign.JUSTIFY))
])
layout = Layout(root_container)

kb = KeyBindings()
@kb.add('q')
def quit(event):
    event.app.exit()


app = Application(layout=layout, full_screen=True, key_bindings=kb)
app.run()

The resulting VSplit looks like this and the surrounding Frame is broken:

┌──────────────────────────────────────────────────────────────────────────────┐
│<   Yes    ><    No    ><  Maybe   ><    So    >│
└──────────────────────────────────────────────────────────────────────────────┘

If the correct VSplit width is explicitly specified (e.g., width=78), the surrounding Frame is correct but the buttons are not justified:

┌──────────────────────────────────────────────────────────────────────────────┐
│<   Yes    ><    No    ><  Maybe   ><    So    >                              │
└──────────────────────────────────────────────────────────────────────────────┘

With Window children instead of Button children, the result does seem to be justified, albeit with left-aligned windows. (It is, however, non-functional.)

┌──────────────────────────────────────────────────────────────────────────────┐
│< Yes >             < No >            < Maybe >            < So >             │
└──────────────────────────────────────────────────────────────────────────────┘

The expected/desired result is to have working, justified buttons:

┌──────────────────────────────────────────────────────────────────────────────┐
│<   Yes    >          <    No    >          <  Maybe   >          <    So    >│
└──────────────────────────────────────────────────────────────────────────────┘

This was observed on prompt-toolkit-3.0.23 on Ubuntu 20 LTS.

This is most likely user error of some sort, but I am not able to figure out how to specify this desired result.

Thanks for the great toolkit, and any insight on this issue!

Reproduce the issue with the provided Application, HSplit, VSplit, Frame, Window, FormattedTextControl, and Button example on prompt-toolkit 3.0.23. Start by tracing how VSplit measures Button children and how Frame derives its width; compare that with Window children and an explicit width. Done means working buttons remain justified across the full frame without breaking the surrounding border.