Its a problen with sub-d's when coverting from polys alias has to fix it, happens to me a lot to. There are 3 ways to fix it.

1) If you want a quick fix, go sudiv surface, clean topology. Keep it mind it only fixes it for the duration you are using that file that time, if you shut down maya and re-open the spots will return.

2) More perminate fix, go subdiv surface, collapse hierarchy, I just leave the options at default. This will make a duplicated sub-d of your head, but the only problem is it will be a little heavier in geometry. The spots should be fixed.

3) Perminate fix, do all your work in sub-d, modelling , blendshapes et. when finished, covert back to poly's smooth it 1 or 2 levels and bind it that way.

Hope that helps. Nice model by the way.

Kurt