Tab titles not rendering as expected

I’m trying to place an object (ideally a row of widgets) above a bunch of tabs, but when I do the tab titles stack on top of each other. This is what I’d like produce:

But this is what I’m getting:

Any suggestions for what I am doing wrong? Is this a bug that I should report? Below is the MWE:

from os.path import dirname, join

from import curdoc
from bokeh.layouts import row, column, widgetbox, Spacer
from bokeh.models import ColumnDataSource, Legend
from bokeh.models.widgets import PreText, Select, Paragraph
from bokeh.models.widgets import TextInput, HTMLTemplateFormatter, StringFormatter, Div
from bokeh.models.widgets import CheckboxGroup, DataTable, TableColumn
from bokeh.models.widgets import Panel, Tabs, Button
from bokeh.plotting import figure
from bokeh.palettes import Viridis4, Blues4

testbutton1 = Button(label=“Test Button”)
testbutton2 = Button(label=“Test Button”)
testbutton3 = Button(label=“Test Button”)
testbutton4 = Button(label=“Test Button”)
testbutton5 = Button(label=“Test Button”)
testbutton6 = Button(label=“Test Button”)
testbutton7 = Button(label=“Test Button”)

create tabs using Panel

tab1 = Panel(child = testbutton1, title = ‘Panel 1’)
tab2 = Panel(child = testbutton2, title = ‘Panel 2’)
tab3 = Panel(child = testbutton3, title = ‘Panel 3’)
tab4 = Panel(child = testbutton4, title = ‘Panel 4’)
tab5 = Panel(child = testbutton5, title = ‘Panel 5’)
tab6 = Panel(child = testbutton6, title = ‘Panel 6’)

layout = column(testbutton7,Tabs(tabs = [tab1,tab2,tab3,tab4,tab5,tab6]))