vb.org Archive - Disappearing search results

I have the maximum search results displayed set to 500 on my site.

When searching my recently 'upgraded' forum (from 3.6.8 to 4.2.2) for common words, the search does say it has found 500 and says there are 20 pages of results. Problem is, when you click on page 2, 3, 4 etc as users are doing so the results number in the bottom left goes down. The result now leaving approximately 12 pages of 300 results.

My site has 3 million posts so I though it was maybe a problem with the search function. I have now installed Sphinx search which is blisteringly quick but, the same problem is still occurring.

Any ideas folks?

--------------- Added [DATE]1382563163[/DATE] at [TIME]1382563163[/TIME] ---------------

I have seen this issue on other sites, has anyone managed to work out the cause?

X vBulletin 3.8.12 by vBS Debug Information
Template Usage: (1)ad_footer_end (1)ad_footer_start (1)ad_header_end (1)ad_header_logo (1)ad_navbar_below (1)footer (1)gobutton (1)header (1)headinclude (6)option (1)post_thanks_navbar_search (1)printthread (1)printthreadbit (1)spacer_close (1)spacer_open Phrase Groups Available: global postbit showthread	Included Files: ./printthread.php ./global.php ./includes/init.php ./includes/class_core.php ./includes/config.php ./includes/functions.php ./includes/class_hook.php ./includes/modsystem_functions.php ./includes/class_bbcode_alt.php ./includes/class_bbcode.php ./includes/functions_bigthree.php Hooks Called: init_startup init_startup_session_setup_start init_startup_session_setup_complete cache_permissions fetch_threadinfo_query fetch_threadinfo fetch_foruminfo style_fetch cache_templates global_start parse_templates global_setup_complete printthread_start bbcode_fetch_tags bbcode_create bbcode_parse_start bbcode_parse_complete_precache bbcode_parse_complete printthread_post printthread_complete
Messages:

X vBulletin 3.8.12 by vBS Debug Information

Page Generation 0.02423 seconds
Memory Usage 1,699KB
Queries Executed 10 (?)

More Information

Template Usage:

(1)ad_footer_end
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(1)ad_header_end
(1)ad_header_logo
(1)ad_navbar_below
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(1)gobutton
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(6)option
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Phrase Groups Available:

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./printthread.php
./global.php
./includes/init.php
./includes/class_core.php
./includes/config.php
./includes/functions.php
./includes/class_hook.php
./includes/modsystem_functions.php
./includes/class_bbcode_alt.php
./includes/class_bbcode.php
./includes/functions_bigthree.php

Hooks Called:

init_startup
init_startup_session_setup_start
init_startup_session_setup_complete
cache_permissions
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Messages:

X vBulletin 3.8.12 by vBS Debug Information
Page Generation 0.02423 seconds Memory Usage 1,699KB Queries Executed 10 (?)
More Information
Template Usage: (1)ad_footer_end (1)ad_footer_start (1)ad_header_end (1)ad_header_logo (1)ad_navbar_below (1)footer (1)gobutton (1)header (1)headinclude (6)option (1)post_thanks_navbar_search (1)printthread (1)printthreadbit (1)spacer_close (1)spacer_open Phrase Groups Available: global postbit showthread	Included Files: ./printthread.php ./global.php ./includes/init.php ./includes/class_core.php ./includes/config.php ./includes/functions.php ./includes/class_hook.php ./includes/modsystem_functions.php ./includes/class_bbcode_alt.php ./includes/class_bbcode.php ./includes/functions_bigthree.php Hooks Called: init_startup init_startup_session_setup_start init_startup_session_setup_complete cache_permissions fetch_threadinfo_query fetch_threadinfo fetch_foruminfo style_fetch cache_templates global_start parse_templates global_setup_complete printthread_start bbcode_fetch_tags bbcode_create bbcode_parse_start bbcode_parse_complete_precache bbcode_parse_complete printthread_post printthread_complete
Messages: