Mute Bug? Within Studio One Pro 3.5.1

If I use Audio Tracks.. and for example I mute with my Faderport 8 track nr.1 the track gets muted and you see the red M in arrange view also in the mixer view.

But if you use a instrument for example in track 1 and you mute with the Faderport 8 ..you hear that the audio get's muted but you don't see any visual indication in the arranger view.. only if you open up the mixer...then you see the red M.