I just thought I'd post this in case anyone else sees it and thinks there's something wrong with their mouse.

Normally, left clicking on the tempo up/down arrows changes the tempo by 5 BPM. Right clicking changes it by 1 with each click. However, sometimes the first click of the left mouse button will change it by 1 BPM. I have verified this carefully. I can usually get it to happen by changing the key, loading a new tune, and recording some melody.