This is a common behavior I have observed, since I did it myself, but I found some kind of solution.
When there are i.e. 5 people in the server, but 3 are AFK and 2 are actually playing, they can't use the vote system to change the map, I see this as an issue.
My solution to this as a player is, to go spec when I'm alt-tabbed or just AFK, but as a server side request, I propose this change:
- To send AFK (after # time of inactivity) people to spectators.