I've found this bug on Dota 6.57b playing Single Draft (-sd) mode. When you pick your desired hero, other heroes icon removes. But If you share your units to your Allies, your allies will be able to pick the remaining two heroes from your Circle Of power. And your allies can do same thing and so then if all team share their units they will have a choice of picking 1 hero from all teamates total 15 heroes. Also you can swap heroes :)
According to me its a bug becuase it wasn't possible in older maps.