Vince,
I too have seen the same after using disavow. I did not have a manual penalty, but noticed some ranking drops related to Penguin, or Panda, or whichever was spammy links. I got rid of a bunch of low quality links and noticed a drop, not instantly but after about 1 month.
My question for you Vince, is have you seen an improvement since then? I am hoping you have!