On the
GW site there is this
"Speaking of that, you should make a point to detach the Gun Drones on your Devilfish and other tanks. They are part of most vehicle profiles, so they are effectively 'free' units. Plus, they increase the number of targets the enemy must kill to destroy the vehicle."
http://uk.games-workshop.com/tau/tactics-basics/6/ I never saw the gun drone like that before. Is this again a tactica with error or the rules support that? You hide the drones in the corner and you don't score any point for destroying devilfish until the drones are dead ?
For those without the codex the devilfish and pirahna are silent about that. The gun drones rules that may apply say
"drones may disengage in the same way as infantry dismount from a transport and form an independant unit. From then on the gun drones function as a gun drone squadron. "
"will never count as a scoring unit"
"are treated as passenger if the vehicle is damaged"