Volume automation accidentally changed

I’m having a frustrating issue with Cubase 7, often times, a track goes silent and the cause is that its drop down subtrack, which defaults to Volume, has been turned all the way down. Again, this happens often, and if I am “doing it”, I have no idea how I am doing it. It may be related to the mouse wheel. I don’t intend to edit volumes in this subtrack, and yet they are frequently edited, as if by themselves, causing the track to go silent.

Anyone else experience this, and/or have any advice?