Quoted from Craig:I'll double check this evening (or sometime very soon, at any rate). I had the impression that it was doing nothing at all (that is, that the knocker didn't go off and it didn't add a credit), but I could be completely wrong.
FWIW mine does this, and as it was home play only I decided to never investigate further (literally, IF the only not working was a single special strike that is very rarely used on my 3 ball game... I am okay with that).
IF it is a missing feature, that is actually surprising!