Hi Sanskruti,
The problem here is that your dropdown has only 5 values in total and you have put 6 as the number of items to display.
Not sure if this is how the widget works or if it is a bug, but if you have put up lets say n items to display then your list should have atleast n+1 items otherwise it would not show the selected items as comma separated.
So in your case, if your list has only 5 items then put 4 as number of items to display, because once all 5 have been selected it would show as All selected, irrespective of your configuration.