Cluster jewels scalable or not?

I have seen some builds which uses multiple times the same passive skill of a medium cluster jewel. In game this is marked as not scalable but in PoB it is the case?

Example:

Remarkable
8% increased Cast Speed with Brand Skills
Skills which create Brands have 35% chance to create an additional Brand

?
8% increase can be used multiple times when using multiple jewels with "remarkable" in the build.

Is this a bug in Poe or PoB?

You can stack them. A few notables have global limits that you cannot stack beyond. Purposeful Harbinger is one example.

Anything "up to X%" is a limit shared among all cluster jewel notables. Otherwise you can have as many of the same notable throughout your jewels as you can fit.

With the notable you mentioned, I believe it's capped at 100% to spawn an additional brand (I may be wrong and it could start creating 3+ brands with more than that but I doubt it). The cast speed stacks forever though.

Thx