June,
I spent a few hours narrowing this down and I know what is going on. The query is using the parcel you search for and looking to find if any other parcels intersect it, in the case of someone wanting to find overlapping polygons in the same layer. I believe the way features are being generalized for the web, the two parcels do slightly overlap. The app is already using the GeometryEngine to filter out non overlapping features returned by the query, but it does not check for features who have a very small overlap. In this case, 3.6 sq feet.
I can code to remove very small overlaps, but what is the threshold and should we expose this option
I can also code to not look for overlap on the searched feature.
I have tested both options and they resolve your issue, but I need to make sure I do not break and existing apps.