Webpart zone index always gives 0

Question

I'm having some problems with placement of my web parts. I have two different CEWP, which should be placed with zone index 0 and 1. However, after deployment both have the index 0. This is how I set the index in code:

            using (SPWeb web = site.OpenWeb())
            {
                SPLimitedWebPartManager webparts = web.GetLimitedWebPartManager(pageUrl, PersonalizationScope.Shared);
                var wp = new ContentEditorWebPart();
                wp.Hidden = false;
                wp.ContentLink = web.Site.ServerRelativeUrl + "SiteAssets/imageMap.html";
                wp.ChromeType = PartChromeType.None;
                webparts.AddWebPart(wp, "left", 1);
                webparts.SaveChanges(wp);
                web.Update();
            }
        }

How can I make the zone index "stick"?