Hi Roger, that's a common problem with the Blend Command, because right now it can't blend "broken" edges, but only single looped ones.
One possible solution is to divide each edge in the the same number of segments.
In this case I trimmed the edge of the neck using Trim with Add Trim Points option checked, splitting it in six segments, just as the body edge.
Then I blended each couple of edges separately and joined the resulting surfaces.
Hope it helps.
Cheers
Daniele