There's a good reason for that, assuming you understand game mechanics.
Hint: Anyone who plays a red by Yew gate could tell you exactly why Scalis isn't guard whacked.
Well, and for those who do not play a red at Yew Gate ?
Are you saying that Scalis is inside the Guard zone and yet left unarmed by the Guards ??
If so, I see this as a bug.
The reason for a Guard zone, as I see it, is to have Guards intervene to any and all threats to players within a Guard zone. If they do not, even though there does is a threat, and that threat does is within a guard zone well, then something here is mulfunctioning, IMHO.