Mmmm, it was designed to add/remove the items with the status selected to the results.
If you had only green (open) items, and you click on yellow circle (pending), it will add the pending to the list, so that open (green) and pending (yellow) will be shown.
If you want to see only the pending ones, and you were seing the open ones, then you need to click twice: once at the yellow circle to add the pending (yellow) items to the list of results, and another time on the green circle, to hide the open items from the list.
What is pending to fix is a way to indicate which status filters are active.
https://dev.tiki.org/item5984 - "15.x UI Regression: no visual indication of which tracker item status filters are applied"