[Python] Why does the button recognize clicks despite deactivation?

Program outline: show a helpfile (PDF) on button click -> runs well

But if I press the button even though the file is still open, the frontend remembers this and then opens the file as often as it was clicked as soon as I close the helpfile. So I decided to deactivate the button.

Unfortunately it did not help. It remembers every click until the program crashes.

def openHelpfile():
helpfile_btn.config(state=DISABLED)
os.system("helpfile.pdf")
helpfile_btn.config(state=NORMAL)

## FRONTEND =====================
main_window = Tk()
main_window.protocol("WM_DELETE_WINDOW", close_window)
style = Style("darkly")
main_window.title("SPC Tool: Pyro v4")
main_frame = Frame(main_window)
main_frame.pack(padx=10, pady=10)

status_frame = LabelFrame(main_frame, text="Programm Status")
status_frame.grid(row=3, column=0, sticky="ew", pady=5)
statusbar = Text(status_frame, height=1, width=1, font=("", 8, "normal"))
statusbar.pack(side="left", expand=True, fill="both", padx=10, pady=10)
helpfile_btn = Button(
status_frame,
text="?",
command=openHelpfile,
width=5,
bootstyle="-secondary-outline",
)
helpfile_btn.pack(side="right", padx=10, pady=10)

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