I originally reported this as and it turned out to be a display template bug. It wasn't the case that attributes were repeating for every splitter match.
However, now this does appear to be happening.
I'm working on the Lightwork import, and for repeating elements on the entity editor, like Nationality and Cultural Heritage, the attribute values get added every single time the entitySplitter finds a match on labels.
In the above example, the value "Welsh" in the Nationality element is added once for every single time the entities name appears in the object data.