When working on one midi region, others become muted

Is this a bug? When I start adding notes in a midi region, the other midi tracks in my project become silent when I next play the project. The trick is I then just click on a blank area of the project and start playing the project again and everything becomes audible again. Annoying.

Anyone else?

If the MIDI editor has focus, it is switched to solo.
You can deactivate it.