When using the following documentation to implement a custom Search Results widget: 

https://www.progress.com/documentation/sitefinity-cms/for-developers-customize-search-results-by-overriding-the-searchresults-class-webforms

and trying to sort the results using Linq, the results shown are different when paging and when showing All the results in the same page:

 

public IEnumerable<IDocument> Search(string query, string catalogue, string[] searchFields, string[] highlightedFields, int skip, int take, out int hitCount)
{
    var control = this.control;
    var service = Telerik.Sitefinity.Services.ServiceBus.ResolveService<ISearchService>();
    var queryBuilder = ObjectFactory.Resolve<IQueryBuilder>();

    var searchQuery = queryBuilder.BuildQuery(query, control.SearchFields);
    searchQuery.IndexName = catalogue;
    searchQuery.Skip = skip;
    searchQuery.Take = take;
    searchQuery.OrderBy = null;
    searchQuery.HighlightedFields = control.HighlightedFields;

    var result = service.Search(searchQuery);
    var orderedList = result.OrderByDescending(l => l.GetValue("PublicationDate")).ToList();

    hitCount = result.HitCount;
    return orderedList.SetContentLinks();
}

 

Lucene returns a different set of records based on the properties passed via the search query. 

Sorting expressions need to be defined in the SearchQuery object passed to Search method of the SearchService.

E.g: 
 

searchQuery.OrderBy = new string[] { "PublicationDate DESC" };

The code would look like this: 
 

var control = this.control;
var service = Telerik.Sitefinity.Services.ServiceBus.ResolveService<ISearchService>();
var queryBuilder = ObjectFactory.Resolve<IQueryBuilder>();

var searchQuery = queryBuilder.BuildQuery(query, control.SearchFields);
searchQuery.IndexName = catalogue;
searchQuery.Skip = skip;
searchQuery.Take = take;
searchQuery.OrderBy = new string[] { "PublicationDate DESC" };
searchQuery.HighlightedFields = control.HighlightedFields;



var result = service.Search(searchQuery);

hitCount = result.HitCount;

return result.SetContentLinks();