Checkbox not checking

[raquelct]

I have a simple code to test this widget but my checkboxes uncheck when i release the click on a item of the list, they just keep checked while I'm holding the mouse button pressed.
Is somithing wrong with my code or is it a bug?

from tkinter import *
from tkinter import ttk
from checklistcombobox import ChecklistCombobox

root = Tk()
ccb = ChecklistCombobox(root,state='readonly',checkbutton_height=1,width=30,values=["a","b","c"])
ccb.pack()
root.mainloop()