I ran into a problem with the permissions system. I'm using host groups like these [00001] prompt or [06556] kalorama. This is working fine through the whole system.
Now i created a new user, new group, added the user to the group and tried to add one of the host groups to the user group I've created.

You can select the host group and save it without any problems. When i go back to the user group to review my actions, the lists are empty. At first i thought is was a permission problem in the hosts but its not. When i rename the group from [00001] Prompt to Prompt and add it to the user group everything works as expected.

The naming i use is something we use to generate reports for hosts and items so its something we like to keep using.

I upgraded the Zabbix gui from 1.8.2 to the 1.8.3 svn (revision 13391) and the problem remains.