parallel foreach stuck on 8 workUnitSize

[Booster]

https://dlang.org/library/std/parallelism/task_pool.parallel.html#workUnitSize

Basically have no difference than the above but when I change the 
workUnitSize to 1, 4, whatever it is always running 8 parallel 
loops.

Either a bug or workUnitSize is not what I think it is. I simply 
want to execute n iterations of the loop at the time, not fixed 
at 8.