I don't know if this is common knowledge but I noticed this today at a red light. Owned the car for 7.5 years and never noticed this. It only concerns me if its a symptom to a bad solenoid or something, anyone know? Lol.

 

Normal to an extent. When you push the brake pedal, air moves from the booster into the intake manifold. So it can affect the fuel trims a little bit. I haven't looked to see if that amount is normal for every LNF but some variation is to be expected.