Rotation Constraints offset world axis lock

Yesterday when I was making the body part of my rig I needed to make a bone going along global z. When the spines bones was complete, I made the copy rotation constraints and putt on offset the bone is snapped to matching the global axis(it rotates 90° local x). When I turn off the influence off the constraint the bone turns back. It also only happened in world space not local space.
Is this a bug or is it something that is supposed to happed?

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