Siteadmin fulltext search

Hi

We've found a problem with siteadmin fulltext search. For the first page paging is completely ignored as 44 Mb with 7000 results are downloaded although only 15 results are needed. It took approximately 3 minutes. An investigation revealed that if the "orderby" parameter from the post-request is removed the search downloads only 15 results and does it much faster of course.

The question is why the "orderby" parameter makes CQ return 7000 results instead of 15 needed for the first page?

Thanks