I'm trying to wrap my head around this bug and want to know if I have it correct, wrong, or there is more to it.
1) The bug exist regardless of being tournament, normal province or spire battles. I haven't read anyone confirm this. It just doesn't seem like the battle engine would only manifest the bug in one case, but not the others.
2) Only enemy troops that could be produced in the training grounds or mercenary camp are affected, regardless of your ability to produce them. Troops that are produced in the barracks or their province troops are not affected.
3) The affect is any boost you have which benefits that type of troop also boosts theirs. However, the boost doesn't show in their stats, just in the damage they deliver to you or the reduced damage you deliver to them.
4) The boost provided by the fire phoenix, AWs, and 5-day buildings are all imparted to their troops.
5) It doesn't matter what type troop they are attacking or being attacked by, they have the boost. In other words, it's not limited to fights between the same type units, such as LR to LR.
6) If you look at what troops they will be bringing to the battle and you go back to your city and disconnect all buildings that would help those, they lose that boost, as would your troops. Of course this is cumbersome and you would have to delete any 5-day buildings, so it's not practical, but it would remove their boost. I also don't know if disconnecting the fire phoenix would remove it's bonus.