I was disconnected due to Inactivity while I was dead spectating my friend in combat. This was no more then 5 minutes, but even so I think it's kind of odd that you can be Marked for Inactivity while you are dead.
Same happened to me. I lost against my opponent in Brawl but my team-mate was doing really well against him, taking his time and pacing his attacks. it was so close, and I got kicked for inactivity, so I quit playing. This is a ridiculous mechanic, I'm not inactive, I'm spectating. Fix this.