sometimes can't end list by hitting return twice (IE, Edge)

[bill]

On IE (tested on IE8-IE11) and also Edge, load test_Editor.html and then:

(1) Clear text of second editor and type:

start
end

(2) In between "start" and "end" create a list by clicking the [123] toolbar button, and type some list items:

start
   1. a
   2. b
   3. c
end

(3) Hit return a few times. The expected behavior (and actual behavior on Chrome) is to end the list:

start
   1. a
   2. b
   3. c

end

But on IE and Edge the behavior is:

start
   1. a
   2. b
   3. c
   4.
   5.
end