title: Why is there a dash in ttk radio button when made with a function?
body: <p>When I make two sets of the same radio buttons there will be a dash in one of the buttons created from a function.</p>
  <pre><code>import tkinter as tk
  from tkinter import ttk
  
  
  def add_radio_buttons():
      a_b = tk.StringVar()
      a_button = ttk.Radiobutton(window, text=&quot;A&quot;, value=&quot;A&quot;, variable=a_b)
      a_button.grid(row=1, column=1)
      a_button.invoke()
      b_button = ttk.Radiobutton(window, text=&quot;B&quot;, value=&quot;B&quot;, variable=a_b)
      b_button.grid(row=1, column=2)
  
  
  window = tk.Tk()
  
  add_radio_buttons()
  
  a_b_too = tk.StringVar()
  a_button = ttk.Radiobutton(window, text=&quot;A&quot;, value=&quot;A&quot;, variable=a_b_too)
  a_button.grid(row=2, column=1)
  a_button.invoke()
  b_button = ttk.Radiobutton(window, text=&quot;B&quot;, value=&quot;B&quot;, variable=a_b_too)
  b_button.grid(row=2, column=2)
  
  window.mainloop()
  </code></pre>
  <p>Is this a bug or am I forgetting something?</p>