This is used on purpose. The player has to be a valid war target. Typical use involves their largest player parking a defensive primarch on your castle. As that player is unlikely to have flames against them, and their primarch will be difficult to kill.
Often used with a ton of 1 troop primarchs to keep enfeeble from working and generate more defends.
It’s both terrible and clever. Personally I won’t use it as it seems underhanded to involve troops in a main game war. To me it says “we can’t win without.” I also prefer not having it done to us more.
All attacks on a valid war target count no matter if main game or or atlas or whatever. They stop counting when the defender has 5 flames against them or the attacker already has 5 flames on someone. (I think both stop it, but it might just be one of the two that works)