when you dropped the db on proxy, what exact data did you insert in it (besides schema) ?
I didn't insert anything, just did "mysql zabbix < database/mysql/schema.sql" and then launched zabbix_proxy.
Could you give the output of next queries on server database:
select * from groups where groupid = 0;
select configid,refresh_unsupported,discovery_groupid,snmptrap_logging from config;
show create table config;
mysql> select * from groups where groupid = 0\G;
Empty set (0.00 sec)
mysql> select configid,refresh_unsupported,discovery_groupid,snmptrap_logging from config\G
*************************** 1. row ***************************
configid: 1
refresh_unsupported: 600
discovery_groupid: 0
snmptrap_logging: 1
1 row in set (0.00 sec)
mysql> show create table config\G;
*************************** 1. row ***************************
Table: config
Create Table: CREATE TABLE `config` (
`configid` bigint(20) unsigned NOT NULL,
`alert_history` int(11) NOT NULL DEFAULT '0',
`event_history` int(11) NOT NULL DEFAULT '0',
`refresh_unsupported` int(11) NOT NULL DEFAULT '0',
`work_period` varchar(100) NOT NULL DEFAULT '1-5,00:00-24:00',
`alert_usrgrpid` bigint(20) unsigned DEFAULT NULL,
`event_ack_enable` int(11) NOT NULL DEFAULT '1',
`event_expire` int(11) NOT NULL DEFAULT '7',
`event_show_max` int(11) NOT NULL DEFAULT '100',
`default_theme` varchar(128) NOT NULL DEFAULT 'originalblue',
`authentication_type` int(11) NOT NULL DEFAULT '0',
`ldap_host` varchar(255) NOT NULL DEFAULT '',
`ldap_port` int(11) NOT NULL DEFAULT '389',
`ldap_base_dn` varchar(255) NOT NULL DEFAULT '',
`ldap_bind_dn` varchar(255) NOT NULL DEFAULT '',
`ldap_bind_password` varchar(128) NOT NULL DEFAULT '',
`ldap_search_attribute` varchar(128) NOT NULL DEFAULT '',
`dropdown_first_entry` int(11) NOT NULL DEFAULT '1',
`dropdown_first_remember` int(11) NOT NULL DEFAULT '1',
`discovery_groupid` bigint(20) unsigned NOT NULL,
`max_in_table` int(11) NOT NULL DEFAULT '50',
`search_limit` int(11) NOT NULL DEFAULT '1000',
`severity_color_0` varchar(6) NOT NULL DEFAULT 'DBDBDB',
`severity_color_1` varchar(6) NOT NULL DEFAULT 'D6F6FF',
`severity_color_2` varchar(6) NOT NULL DEFAULT 'FFF6A5',
`severity_color_3` varchar(6) NOT NULL DEFAULT 'FFB689',
`severity_color_4` varchar(6) NOT NULL DEFAULT 'FF9999',
`severity_color_5` varchar(6) NOT NULL DEFAULT 'FF3838',
`severity_name_0` varchar(32) NOT NULL DEFAULT 'Not classified',
`severity_name_1` varchar(32) NOT NULL DEFAULT 'Information',
`severity_name_2` varchar(32) NOT NULL DEFAULT 'Warning',
`severity_name_3` varchar(32) NOT NULL DEFAULT 'Average',
`severity_name_4` varchar(32) NOT NULL DEFAULT 'High',
`severity_name_5` varchar(32) NOT NULL DEFAULT 'Disaster',
`ok_period` int(11) NOT NULL DEFAULT '1800',
`blink_period` int(11) NOT NULL DEFAULT '1800',
`problem_unack_color` varchar(6) NOT NULL DEFAULT 'DC0000',
`problem_ack_color` varchar(6) NOT NULL DEFAULT 'DC0000',
`ok_unack_color` varchar(6) NOT NULL DEFAULT '00AA00',
`ok_ack_color` varchar(6) NOT NULL DEFAULT '00AA00',
`problem_unack_style` int(11) NOT NULL DEFAULT '1',
`problem_ack_style` int(11) NOT NULL DEFAULT '1',
`ok_unack_style` int(11) NOT NULL DEFAULT '1',
`ok_ack_style` int(11) NOT NULL DEFAULT '1',
`snmptrap_logging` int(11) NOT NULL DEFAULT '1',
`server_check_interval` int(11) NOT NULL DEFAULT '60',
PRIMARY KEY (`configid`),
KEY `c_config_1` (`alert_usrgrpid`),
KEY `c_config_2` (`discovery_groupid`),
CONSTRAINT `c_config_1` FOREIGN KEY (`alert_usrgrpid`) REFERENCES `usrgrp` (`usrgrpid`),
CONSTRAINT `c_config_2` FOREIGN KEY (`discovery_groupid`) REFERENCES `groups` (`groupid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
And what does next one return (also server database)?
select * from groups where internal=1;
mysql> select * from groups where internal=1;
Empty set (0.00 sec)
Oh, nice. What about:
select * from groups;
If that is too big list could you paste it on some pastebin service?
mysql> select * from groups; +---------+-----------------------------------------+----------+ | groupid | name | internal | +---------+-----------------------------------------+----------+ | 1 | Templates | 0 | | 10 | 10.5 | 0 | | 11 | 10.4 | 0 | | 13 | 10.6 | 0 | | 15 | 10.8 | 0 | | 16 | 10.9 | 0 | | 17 | 10.10 | 0 | | 22 | 10.11 | 0 | | 23 | 10.12 | 0 | | 24 | 10.1 1 | 0 | | 25 | 10.1 2 | 0 | | 26 | 10.1 3 | 0 | | 27 | 10.1 4 | 0 | | 28 | 10.1 5 | 0 | | 29 | 10.1 6 | 0 | | 30 | 10.2 1 | 0 | | 31 | 10.2 2 | 0 | | 32 | 10.2 3 | 0 | | 33 | 10.2 4 | 0 | | 34 | 10.2 5 | 0 | | 35 | none | 0 | | 36 | 10.6 | 0 | +---------+-----------------------------------------+----------+ 22 rows in set (0.00 sec)
Could you also give the output of this:
show variables like 'FOREIGN_KEY_CHECKS';
It's on.
mysql> show variables like 'FOREIGN_KEY_CHECKS'\G
*************************** 1. row ***************************
Variable_name: foreign_key_checks
Value: ON
1 row in set (0.00 sec)
Did you turn off foreign key checks at some point? Because this is the only way I could have unreferenced groupid in config table.
mysql> show variables like 'FOREIGN_KEY_CHECKS';
+--------------------+-------+
| Variable_name | Value |
+--------------------+-------+
| foreign_key_checks | ON |
+--------------------+-------+
1 row in set (0.00 sec)
mysql> select * from groups where groupid=0;
Empty set (0.04 sec)
mysql> insert into config (configid,refresh_unsupported,discovery_groupid,snmptrap_logging) values (1,600,0,1);
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`dimir_test`.`config`, CONSTRAINT `c_config_2` FOREIGN KEY (`discovery_groupid`) REFERENCES `groups` (`groupid`))
mysql> SET FOREIGN_KEY_CHECKS = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> insert into config (configid,refresh_unsupported,discovery_groupid,snmptrap_logging) values (1,600,0,1);
Query OK, 1 row affected (0.04 sec)
mysql> SET FOREIGN_KEY_CHECKS = 1;
Query OK, 0 rows affected (0.00 sec)
mysql> select configid,refresh_unsupported,discovery_groupid,snmptrap_logging from config;
+----------+---------------------+-------------------+------------------+
| configid | refresh_unsupported | discovery_groupid | snmptrap_logging |
+----------+---------------------+-------------------+------------------+
| 1 | 600 | 0 | 1 |
+----------+---------------------+-------------------+------------------+
1 row in set (0.00 sec)
So, when setting foreign key checks to on MySQL does not check constraints.
In order for you to fix the problem:
1) stop server and proxy
2) run next SQL queries on the server database
INSERT INTO `groups` (`groupid`,`name`,`internal`) values ('5','Discovered hosts','1');
UPDATE `config` set discovery_groupid=5;
3) empty (or recreate) proxy database
4) start server and proxy
The problem should go away.
Yes, i think i have disabled them before running "upgrades/dbpatches/2.0/mysql/upgrade" (in patch.sql) because otherwise it failed to run complaining about foreign keys.
So it seems it had broke the constraints. Any idea how to fix it now? 
Aaaah, you shouldn't have done that. You can try this:
http://stackoverflow.com/questions/2250775/force-innodb-to-recheck-foreign-keys-on-a-table-tables
In the future, if you have such errors, report them to us. I'm closing the bug now, feel free to re-open if you disagree.