Undesired result trying to grab first attachment from thread

[N8]

From this Mod: https://vborg.vbsupport.ru/showthread.php?t=271131

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I need this code to always grab the first uploaded file, but for some reason it *sometimes* uses the first uploaded image, but other times it uses other images...



Location: threadbit_process

global $forumids_included; 
if ($vbulletin->options['chip_threadthumb_turn'] AND in_array($foruminfo['forumid'], array_keys((array)$forumids_included))) 
{             
    $have_thumb = false; 
    //using image of first post + youtube thumbnails 
    if ( strpos($vbulletin->options['chip_threadthumb_types'], '1') !== false ) 
    { 
        if (preg_match('#\[IMG\](.+?)\[\/IMG\]#i', $thread['thumb'], $m)) 
        { 
            $thread['thumb_src'] = $m[1];     
            $have_thumb = true; 
        } 
        elseif (preg_match('#\[YOUTUBE\]([^\[]+?)\[\/YOUTUBE\]#i', $thread['thumb'], $m))     
        { 
            $str = preg_replace('#(http.*watch\?v=)?([^"]+?)(&.*)?#', '$2', $m[1]); 
            $thread['thumb_src'] = 'http://i4.ytimg.com/vi/'.$str.'/default.jpg';     
            $have_thumb = true; 
        } 
        //vb4 
        elseif (preg_match('#\[video=youtube;([^\]]+?)\]#i', $thread['thumb'], $m))  
        { 
            $thread['thumb_src'] = 'http://i4.ytimg.com/vi/'.$m[1].'/default.jpg';     
            $have_thumb = true; 
        } 
    } 

    //using file attach 
    if (  
        !$have_thumb // have not a thumbnails 
        AND $thread['attach'] > 0 //have attach files 
        AND strpos($vbulletin->options['chip_threadthumb_types'], '2') !== false ) 
    { 
        //get attach file - image 
        $attach = $vbulletin->db->query_first(" 
            SELECT attachment.attachmentid, attachment.dateline 
            FROM ".TABLE_PREFIX."attachment AS attachment 
            WHERE attachment.postid = ".$thread['firstpostid']." AND attachment.extension IN ('png', 'jpg', 'jpeg', 'gif', 'bmp')
            LIMIT 1 
        "); 
        if($attach) 
        { 
            $thread['thumb_src'] = $vbulletin->options['bburl'].'/attachment.php?attachmentid='.$attach['attachmentid'].'&thumb=1&d='.$attach['dateline'];     
            $have_thumb = true; 
        } 
    } 
     
    if($vbulletin->options['chip_threadthumb_showdefault'] && !$have_thumb) 
    { 
        $thread['thumb_src'] = $stylevar['imgdir_misc'].'/'.$vbulletin->options['chip_threadthumb_noimg'];     
        $have_thumb = 1; 
    } 
    if ($have_thumb) 
    { 
        $thread['hasthumb'] = 1; 
        $thread['threadiconpath'] =& $thread['thumb_src']; 
    } 
     
     
    unset($thread['thumb']);

forumdisplay_query

if($vbulletin->options['chip_threadthumb_turn'] AND THIS_SCRIPT == 'forumdisplay' AND $vbulletin->forumcache["$forumid"]['thumb_w']) 
{ 
    $previewfield .= "thread.firstpostid, post.pagetext AS thumb,"; 
    if(!strpos($previewjoin, 'post AS post')) 
    { 
        $previewjoin .= "\nLEFT JOIN " . TABLE_PREFIX . "post AS post ON(post.postid = thread.firstpostid)\n"; 
    } 
}

Anyone know what might be happening here?