I have tried a couple of different variations, and all are having the same issue.
The issue is as follows:
If the user users the enter key to select values, and then hits the tab button in order to move to the next field, the last item selected is removed from the field. I've only been able to produce this on tab, clicking doesn't have this error. Also, selectOnTab:true adds the value if not selected, but once the item is selected with the enter key, tabbing away from the field removes the last item selected. If there is a fix for this let me know, if not, have fun figuring it out! lol.