Plot output with ipywidgets formatting incorrectly

Describe the issue

I built a small GUI within a notebook and had two figures in an ipywidgets HBox object. the latest version of ipympl made it so I could not have both figures in an HBox and generally disrupted the formatting of the object. I was able to fix the issue by reverting both matplotlib and the ipympl versions.

a short script that generates the broken output is as follows

%matplotlib widget
from IPython.display import display, HTML
display(HTML("<style>.container { width:100%!important;}</style>"))

import ipywidgets as ipy
import matplotlib.pyplot as plt
import numpy as np
out1 = ipy.Output()
b1 = ipy.Button(description = 'button1')
b2 = ipy.Button(description = 'button2')
x = np.linspace(0,7,21)
y = np.sin(x)
with out1:
    fig,ax = plt.subplots()
    ax.plot(x,y)
    
display(ipy.HBox([out1,ipy.VBox([b1,b2])]))

Versions

(working version)

ipympl == 0.5.8
matplotlib == 3.3.3

(broken version)

matplotlib == 3.5.1

提供された notebook スクリプトを、一覧にある動作する matplotlib/ipympl バージョンと壊れている matplotlib/ipympl バージョンで実行し、その後 HBox のレイアウトとウィジェットの書式を比較します。影響を受けるバージョンで、図とボタンが HBox 内に一緒に正しくレンダリングされれば完了です。