When deleting given the index "END", a KeyError occur. By changing the order of given the key to be deleted and the decrease of the variable end_num, solves this issue.
I made a commit after to solve another issue and was added to this PR. The problem was that was not possible to change multiple_selection with the function configure().
When deleting given the index "END", a KeyError occur. By changing the order of given the key to be deleted and the decrease of the variable end_num, solves this issue.