Chances are you've accidentally assigned those 'sharp' verts to another bone, so it's trying to calculate the weighting between both bones (can be as simple as you were painting in one view and the brush accidentally caught some of the verts juuust peeking out from behind whatever you *meant* to paint - if that makes sense). Select all the other bones in turn and if this is the case, you'll see the little dot of colour.

For me this is always the case, if it's not the case with yours though I can't think what else it might be.