So, originally, it was adding ability modifier to damage, but not to attack roll, on your off-hand strikes. This got reported many times by many people as having been implemented the wrong way around (You are supposed to have your normal attack bonus to hit, which includes ability modifier, but you don't add the ability modifier to the damage without a feat or extra feature).
Larian seem to have 'fixed' this by removing the ability modifier from your damage roll, but you still do not get it added to your attack roll.
It seems kind of strange given that they're struggling to account for what they view as the whole 'missing isn't fun' problem... when they've got something right here that would see fewer misses if they adhered to the rules as written...
