Please forgive me if this is not a bug, but the wiki does not specify if there are any blocks that are not to be affected by mining fatigue.

In survival with mining fatigue applied to me:

/effect ogradyjd 4 10 255 true

I can still break redstone powder layed on a block on the first hit. I have tried changing the level to any number from 5 and up and redstone "wire" is still breakable. The arm does slow down and other blocks that I have tried are still unbreakable. I'm logging a bug because all documentation I've read either implicitly or explicitly states that all blocks are affected by the mining fatigue effect.

If you need anything else from me for this defect, please let me know.