Building Lucene Search Index - Order of templates does matter!

I've just spent a frustrating 30 minutes trying to figure out why a search of mine wasn't returning the results I expected.

Here's the json that gets passed to my API that is used to search against the search index:

{"pages":

    ["c159f9f7-77b6-42c2-9b35-50279001987e",

     "8c24e1a1-986e-4c01-9c2f-447b89805fd7",

     "b52b3044-f7b0-406d-b3ac-6be5b8148a7f",

     "f2726c5f-3fbc-4b25-8d53-693c0eb50b93",

     "2319ea68-74c6-4ba3-af7b-02a6b766f311",

     "a70eb547-bab6-44c0-97ca-b749ba333561",

     "2685a1f2-7aac-4e99-ba9d-5b05667140a7",

     "6385cf29-2133-4c70-a247-ec0be744db64",

     "37816c10-fb96-45b6-b123-cb815926df97"

    ],"language":"en","PageSize":10}

In my search I pass in a number of GUIDs (pages) which are matched against Ids in the index.  Sounds simple enough!  I had four templates added to my index configuration, three of which where pages and one (the last in the list) was inherited by all the pages:
       

<include hint="list:IncludeTemplate">
  <!--Product Overview Page--> 
  <templateId>{1A1706B9-95AF-408D-ACF6-A158315333F4}</templateId>
  <!--Product Module Detail Page--> 
  <templateId>{1263F902-B309-47B1-BCE5-25305167E15C}</templateId>
  <!--Product Module Landing Page--> 
  <templateId>{ECA7823D-4BA9-4995-836B-85FA90F00481}</templateId>
  <!--Related Product Details--> 
  <templateId>{57F36C1B-9292-4386-96DB-8B87A2FBBE28}</templateId>
</include>

All worked fine until I added another page template id to the list (which also inherited the same template as the other pages).  I added it as the last item in the list:

         

<include hint="list:IncludeTemplate">
  <!--Product Overview Page--> 
  <templateId>{1A1706B9-95AF-408D-ACF6-A158315333F4}</templateId>
  <!--Product Module Detail Page--> 
  <templateId>{1263F902-B309-47B1-BCE5-25305167E15C}</templateId>
  <!--Product Module Landing Page--> 
  <templateId>{ECA7823D-4BA9-4995-836B-85FA90F00481}</templateId>
  <!--Related Product Details--> 
  <templateId>{57F36C1B-9292-4386-96DB-8B87A2FBBE28}</templateId>
  <!--Alternative Text--> 
  <templateId>{82B30165-9698-4E79-8445-9F2BEF315382}</templateId>
</include>

Now if my search json just included page ids for pages that were of the new page template type then my query would return what I expected.  Even if I added some additional page ids but the unique count per template was less than the count for my new one, it still worked as expected.

But as soon as I sent in a request where there were a larger number of one of the original template types, then the result excluded my new template type.  It didn't matter where in the list I put the Ids for new template type they always got excluded. - Weird or what!

As soon as I changed the order of my templates in the index configuration it all worked as expected:

         

<include hint="list:IncludeTemplate">
  <!--Alternative Text--> 
  <templateId>{82B30165-9698-4E79-8445-9F2BEF315382}</templateId>
  <!--Product Overview Page--> 
  <templateId>{1A1706B9-95AF-408D-ACF6-A158315333F4}</templateId>
  <!--Product Module Detail Page--> 
  <templateId>{1263F902-B309-47B1-BCE5-25305167E15C}</templateId>
  <!--Product Module Landing Page--> 
  <templateId>{ECA7823D-4BA9-4995-836B-85FA90F00481}</templateId>
  <!--Related Product Details--> 
  <templateId>{57F36C1B-9292-4386-96DB-8B87A2FBBE28}</templateId>
</include>

For brevity here is the query I used to return the search results:

  using (var searchContext =
                    ContentSearchManager.GetIndex(RelatedProductsSearchIndexName).CreateSearchContext())
            {
                var query = GetBaseQueryForOtherType<RelatedProductSearchResultsItem>(searchContext, language);

                var predicate = PredicateBuilder.False<RelatedProductSearchResultsItem>();

                var predicateCategory = PredicateBuilder.False<RelatedProductSearchResultsItem>();

                if (relatedProductsRequest.Pages.Any())
                {
                    predicateCategory =
                        relatedProductsRequest.Pages.Select(item => new ID(item))
                            .Aggregate(predicateCategory, (current, id) => current.Or(p => p.ItemId == id));

                    predicate = predicate.Or(predicateCategory);
                }

                query = query.Where(predicate);

                if (relatedProductsRequest.ProductId != Guid.Empty)
                {
                    query = query.Where(p => p.ProductPageID == relatedProductsRequest.ProductId);
                }

                count = query.Count();

                return query.Page(relatedProductsRequest.PageNumber, relatedProductsRequest.PageSize)
                    .GetResults()
                    .Hits.OrderByDescending(h => h.Score)
                    .Select(h => h.Document)
                    .ToList();
            }