Recording vocals over a music track

Audacity has been working perfectly until a few weeks ago. Now when I try to record vocal tracks over a musical track, the recording starts at the end of the music track.

I’m guessing that this is on a school computer, and that Audacity has recently been updated.
In current versions of Audacity, to record to a new track, hold down the Shift key while you click the record button (or “Shift + R”).