In 2.0.3 when I try to delete a host from a host group (Configuration->Host Groups) and this group was single for the host I get an error:
One of the objects is left without host group. [CHostGroup.massUpdate]

But in 2.0.4 I can delete it successfully which is wrong and should not be allowed !

Reproduced also in Zabbix 2.0.5rc1-33411 last updated: Tue Feb 5 12:36:16 EET 2013

Broken in rev 31651 - in ZBX-5860