CrossListQueryCache().GetSiteData(contextWeb) throws NullReferenceException on second query?

Question

I have an auqward problem that's been nagging me on and off for half a years time. It turns out, when I'm finally taking a real shot at it that my query throws a NullReferenceException the second time I run the script. The first time I ask for 1 row in return, and the second time I ask for three rows in return and I get "Object reference not set to an instance of an object" on GetSiteData().

I have no idea why?

Source code:

    protected DataTable QueryMyNews(string PropertyValue)
    {
        using (SPSite newsSite = new SPSite(ProtocolHelper.SetContextProtocol(SPContext.Current.Site, SettingsManager.GetSetting(SettingsEnum.NewsUrl))))
        {
            using (SPWeb contextWeb = newsSite.OpenWeb())
            {
                string viewfields = "<FieldRef Name=\"Title\" />";
                viewfields += "<FieldRef Name=\"FileRef\" />";
                viewfields += "<FieldRef Name=\"Comments\" Nullable='TRUE' />";
                viewfields += "<FieldRef Name=\"PublishingPageImage\" Nullable='TRUE' />";
                viewfields += "<FieldRef Name=\"ToppNyhet\" Nullable='TRUE'  />";
                viewfields += "<FieldRef Name=\"_ModerationStatus\" Nullable='TRUE' />";
                viewfields += "<FieldRef Name=\"Organisation\" Nullable='TRUE' />";
                viewfields += "<FieldRef Name=\"Created\" Nullable='TRUE' />";
                viewfields += "<FieldRef Name=\"Audience\" Nullable='TRUE' />";
                viewfields += "<FieldRef Name=\"ArticleStartDate\" Nullable='TRUE'/>";
                viewfields += "<FieldRef Name=\"{61cbb965-1e04-4273-b658-eedaa662f48d}\" Nullable='TRUE' />";
                viewfields += "<FieldRef Name=\"TaskDueDate\" Nullable='TRUE' />";

                CrossListQueryInfo query = new CrossListQueryInfo();
                query.FilterByAudience = true;
                query.ShowUntargetedItems = false;
                query.RowLimit = 3;
                query.WebUrl = SPContext.Current.Site.ServerRelativeUrl;
                query.Lists = "<Lists ServerTemplate=\"850\" />";
                query.Webs = "<Webs Scope=\"SiteCollection\" />";
                query.UseCache = false;
                query.ViewFields = viewfields;

                query.Query +=  "<Where>"+
                                    "<Or>"+
                                         "<Geq>"+
                                            "<FieldRef Name='TaskDueDate' />"+
                                            "<Value IncludeTimeValue='TRUE' Type='DateTime'><Today /></Value>"+
                                         "</Geq>"+
                                         "<IsNull>"+
                                            "<FieldRef Name='TaskDueDate' />"+
                                         "</IsNull>"+
                                    "</Or>"+
                               "</Where>";
                query.Query += "<OrderBy><FieldRef Name=\"Created\" Nullable=\"True\" Type=\"DateTime\" Ascending=\"FALSE\"/></OrderBy>";

                CrossListQueryCache myCache = new CrossListQueryCache(query);

                DataTable audienceAndForvaltning = myCache.GetSiteData(contextWeb); // Object refence not set to an instance of an object