Over and over, I'm getting booted for afk when I choose to walk back to my corpse to rez instead of rez at a graveyard in RBG's. Walking back to your corpse is a perfectly viable tactic when a GY is being farmed or your faction is choked up somewhere. This is fairly recent, so something has changed. Obviously with the number of people still turtling, it hasn't helped actual afk's in the least, so this doesn't seem to be a change the helped that anyway.
You get booted because the system considers you inactive. Check when you get flagged for AFK under the minimap in BGs. It was introduced a while ago to prevent AFKers in ghost form.