On auto-registration of the host, the zabbix server writes initial hostname registration information into SQL table autoreg_host - as hostname information is case-sensitive and this table is preserver when the host is removed from Zabbix front-end the new registration of host with the same hostname, but different case is not propagated into hosts table correctly.

Example

1st registration -> autoreg_host hostname: TesT, hosts table: TesT
– delete host from zabbix front-end, change hostname on the zabbix client from TesT to test
2nd registration -> autoreg_host hostname still TesT, hosts tabe still TesT
– delete host from zabbix front-end, remove hostname from autoreg_host table
3rd registration -> autoreg_host test, hosts table test

This seems to be a bug.

Either remove the host from autoreg_host when removed from front-end or do not preserve autoreg_host table after the host is added to hosts table.

Live long and prosper.