The Web API is reporting an incorrect number of issues for at least one volume.
Note how this volume has seven issues: http://www.comicvine.com/morning-glories/4050-39321/
But if you find that volume using the web API, you'll notice it is only reporting 1 issue in the <count_of_issues> tag:
(Just look for id 39321 in the results)
Most volumes do not have this problem, but it is not the first time I've run into this.