PHP post 变量在提交后不会返回隐藏输入字段的整个字符串值

我有这个隐藏的输入字段，名为loginfo包含这个值，提交后，我只得到一半的值，我把maxlength设置为 20000

<input type="hidden" name="loginfo" value='<?=  $user_log_info ?>' maxlength="2000" />
Cookie Info: a:20:{s:11:"NO_TRACKING";s:4:"true";s:9:"PHPSESSID";s:26:"pvbmhif06sd25584sl75tl7qs3";s:13:"orig_referrer";s:29:"http://dev-sti.planetart.com/";s:5:"email";s:23:"semirindi@planetart.com";s:12:"cookie_check";s:4:"done";s:15:"recently_viewed";s:5:"23795";s:15:"user_last_paper";s:2:"CS";s:24:"user_last_size_RECTANGLE";s:3:"5x7";s:18:"user_last_quantity";s:2:"25";s:7:"cart_id";s:32:"64a0d1346aff6ff6aeb7f6a78c9ad156";s:23:"shopping_cart_tmp_items";s:1:"0";s:23:"shopping_cart_act_items";s:1:"1";s:12:"_uslk_visits";s:1:"1";s:14:"_uslk_referrer";s:29:"http://dev-sti.planetart.com/";s:18:"_uslk_bootstrapped";s:1:"1";s:8:"_uslk_ct";s:1:"0";s:8:"_uslk_co";s:1:"0";s:12:"_uslk_active";s:1:"0";s:22:"_uslk_page_impressions";s:2:"45";s:15:"_uslk_app_state";s:6:"Idle;0";},User ID: 817239, User Name: Semirindi, User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36, 'nUser  IP address: 127.0.0.1, 'nUser session ID: pvbmhif06sd25584sl75tl7qs3,CART ID:64a0d1346aff6ff6aeb7f6a78c9ad156

所以当我做var_dump($_POST['loginfo'])时，我只得到一半的字符串而不是全部。这是var_dump($_POST['info'])的输出..知道为什么吗？

string 'Cookie Info: a:20:{s:11:"NO_TRACKING";s:4:"true";s:9:"PHPSESSID";s:26:"pvbmhif06sd25584sl75tl7qs3";s:13:"orig_referrer";s:29:"http://dev-sti.planetart.com/";s:5:"email";s:23:"semirindi@planetart.com";s:12:"cookie_check";s:4:"done";s:15:"recently_viewed";s:5:"23795";s:15:"user_last_paper";s:2:"CS";s:24:"user_last_size_RECTANGLE";s:3:"5x7";s:18:"user_last_quantity";s:2:"25";s:7:"cart_id";s:32:"64a0d1346aff6ff6aeb7f6a78c9ad156";s:23:"shopping_cart_tmp_items";s:1:"0";s:23:"shopping_cart_act_items";s:1:"1";s:12:'... (length=1057)