+1 Damage on some attacks against Treasure Guardians?

It seems like some of my attacks against the Outlaw Rifleman and the Outlaw Pistolero deal 1 more damage than they should. Below I will include some of the numbers from the game:

Outlaw Rifleman HP before fighting: 270
Villager Ranged Damage: 3
Outlaw Rifleman Resists: 0.3 of ranged damage

Expected Damage:
270 – int(3 * (1 – 0.3)) = 268

Outlaw Rifleman HP after one attack: 267
270 – 267 = 3
Outlaw Rifleman HP after two attacks: 265
267 – 265 = 2
Outlaw Rifleman HP after three attacks: 263
265 – 263 = 2

When I use the Hand Attack from a Villager, instead of the Ranged Attack, I get the following results:

Outlaw Rifleman HP before fighting: 270
Villager Hand Damage: 10
Outlaw Rifleman Resists: none against Hand Damage

Expected Damage:
270 – 10 = 260

Outlaw Rifleman HP after one attack: 260
270 – 260 = 10
Outlaw Rifleman HP after two attacks: 250
260 – 250 = 10
Outlaw Rifleman HP after three attacks: 240
250 – 240 = 10

My question is, is this intended or is it a bug?