Is Corruptor/Reaver's Bone Shield Cooldown bugged?

When I upgraded Bone Shields on my Corruptor to level 5 I got 6 flying around skull effects but it seems they don't regenerate well. Ability description says every 5 turns (for maxed out) 1 piece will regenerate so from 0 to max it should take 30 turns. In my case I don't know why but this shield regenerates after about 140 turns. I tested this also on Reaver and it happens again. Is it bug? Or is it working as intended but BS's description mislead?

Bug tracker?

Perphaps you'd want to post this in the bug tracker instead?
Also, there is already a topic that might help you.