Smaller disks don't spin down after their size "passes" with oversized parity rebuild.

My UNRAID disks spin down when not in use (this works fine).

Also for my monthly parity check, smaller disks spin down after their size "mark" passes.
i.e. In an array with a mix of 4TB disks and 8TB disks, the 4TB disks spin down after 50% of parity check. Even ALL disks spin down if parity happens to be larger than the largest data disk and the check goes in the area where only parity size is.
(I had a 10TB parity with 8TB data disks, pending further disk swaps)

Why this doesn't happen with parity rebuild?

Since the smaller disks do not need to be accessed further, why keep them spinning?
I have an 18TB parity, with a mix of 4TB and 8TB data disks (yes pending more swaps after rebuild) and I am now at 55% (so OVER 8TB mark) and ALL disks (4TB and 8TB) are still spinning.

I would say this is a bug.