Do you mean it's being added
all the time, or just when things are depressed? Because that's expected. We add classes dynamically to all sorts of things in the calculator when they change hover/depressed state. It's hard to diagnose without being able to see a live example, even if it's a minimal repro.
One thing you could try is just start removing DOM and/or application-defined listeners from the surrounding application until the calculator starts working as expected again, which should then give you some clue as to where to look for the culprit.