Not true from my understanding. You simply lose 1 hours of shares, the spike is there because it is still part of one of the 5Nd, when we hit the next block you will notice that your 5Nd chart will change. I also think you will need to have an hours worth of increased hash rate (what ever you lost during that hour) to compensate for the lost hour until that drop in hash rate is no longer considered.
I'm sure Kano or someone else can explain this better than I have. Also my understanding of this might not be 100% (or at all) correct.
EDIT: Kano if my post is completely wrong or misleading please can you delete it.