Bug with Bone Offering? or am I not understanding the mechanic

I think there's a bug with Bone Offering. It doesn't seem to be giving the full amount of Block % as described in the skill description. I have the ascendancy "Mistress of Sacrifice", so Offering skills affect my character too. Bone Offering (L19) is only providing a +20% bonus to block. Shouldn't it be providing +34%?

Character sheet (normal stats):
- 18% chance to Block Attacks.

Character sheet with Bone Offering (L19):
- 38% chance to Block Attacks (only a +20% buff?
- 20% chance to Block Spells (only a +20% buff?

Am I not understanding the mechanic properly or is this a bug?

For reference:

Mistress of Sacrifice (Necromancer Ascendancy)
- 20% increased Skill Effect Duration
- Your Offering Skills also affect you

Bone Offering
- Grants Minions +(25-35)% Chance to Block Attacks

How can I tell if my minions are getting a +20% buff or a +34% buff to block?

Maybe I'm missing something, but why do you only have 18% chance to block normally? Your shield gives 30% and you don¡t have Acrobatics.

Please disregard this post, there is no bug. Everything seems to be working now.

The map I was on must have been giving a -40% chance to block and I didn't notice.