Really great, but a listening issue

My chorus class is rolling out with iPads next week and after only using this app for 10 minutes, I already see myself using this it a lot. My goal is to have each of the students sing all of of the notes in a specific locked octave. Since its recorded visually, I can have the students show me proof that they were able all to do it (especially the students who have trouble matching pitch). The only problem Ive noticed so far is that notes below E3 are registering in the upper octave. Its only "hearing" the overtones in my voice. I was singing D3 and D4 back and forth and all of the notes registered as D4 only.

Vocalcoach125 about Do Re Mi Voice Training