Checking the internal API, the input box is supposed to shake when you enter "Shape" or "Shaped".
(await fetch("https://www.wanikani.com/extra_study/items?ids=7672").then(r => r.json()))[0].auxiliary_meanings
results in
[{"type":"warn","meaning":"Shape","message":"That's possible, but it's not the reading/meaning pair you learned."},
{"type":"warn","meaning":"Shaped","message":"That's possible, but it's not the reading/meaning pair you learned."}]
This is the same bug that was reported here.