Steps:
1. Login to JIRA.
2. Go To issues tab and click "Advanced".
3. Type Summary is or duedate is ". Press space after is to write the next option.

Result:
1. It keep on showing you the autocomplete drop down with option "is not" for operator "is" wherever there is no next value to show.
2. Like if we use the same operator with assignee, this problem is not there.

Expected:
1. Auto complete option should get close when user move to next value in search string.