Assume we have a character who can assume multiple styles at one time (like a Master of Many Styles Monk). Said character has the full line of Shielded Gauntlet Style, and also Upsetting Shield Style. Since Shielded Gauntlet Style says:
While receiving this shield bonus to AC, your gauntlet or spiked gauntlet is treated as a buckler for the purpose of using other feats and abilities
While Upsetting Shield Style says:
You can shield bash with a buckler as if it were a light shield ... While using this style, whenever you successfully deal damage to an opponent with a shield bash using your buckler, that opponent takes a –2 penalty on all attack rolls made against you until the start of your next turn.
So we can count our gauntlet as a buckler, and we can bash with a buckler for Upsetting Shield's attack penalty.
Would our Monk hitting people with his gauntlet apply the penalty to them? Would he possibly have to count the attack as though it were a shield bash with a light shield instead of using the scaling dice Shielded Gauntlet Attack gives?