An interesting find here. Trap attack and defense is affected by your troop attack and defense boost.
In other words: Total Trap Attack Boost = Troop Attack Boost + Trap Attack Boost
(and something similar for trap defense).
This means you should always focus on Troop Attack before focussing on Trap Attack and makes Trap Attack gear much less useful.
This is not stay that you can’t have a troop attack gem and a trap attack gem in the same item – just make sure you prioritise the troop attack gem first.
This kind of makes sense, without this traps would be very ineffective against troops with high levels of defense boosts.
Here are some screenshots:
No Boosts – 1 Trap dies, 0 Troops Die:
Had an error in this screenshot – will redo the battle.