title: Tkinter Menubutton items disapper
body: <p>I have a vallid code</p>
  <pre><code>from tkinter import *
  
  top = Tk()
  
  mb=  Menubutton ( top, text=&quot;CheckComboBox&quot;, relief=RAISED )
  mb.grid()
  mb.menu  =  Menu ( mb, tearoff = 0 )
  mb[&quot;menu&quot;]  =  mb.menu
  
  Item0 = IntVar()
  Item1 = IntVar()
  Item2 = IntVar()
  
  mb.menu.add_checkbutton ( label=&quot;Item0&quot;, variable=Item0)
  mb.menu.add_checkbutton ( label=&quot;Item1&quot;, variable=Item1)
  mb.menu.add_checkbutton ( label=&quot;Item2&quot;, variable=Item2)
  
  mb.pack()
  top.mainloop()
  </code></pre>
  <p>When I click to &quot;CheckComboBox&quot; I see list of items.
  Then I click to &quot;Item1&quot; and list of items disapper and I have to click to &quot;CheckComboBox&quot; many times if I want to choose a few items.</p>
  <p>I want &quot;list of times&quot; don't disappeares after click to Item.</p>
  <p><a href="https://i.stack.imgur.com/dYMlr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/dYMlr.png" alt="enter image description here" /></a></p>