In most parts of Zabbix stuff like $1 can be used e.g.:

Name: Status of process $1
Item key: proc.num[zabbix-agent]

The interface replaces this properly with Status of process zabbix-agent in various views. However when this is being done in the LLD rules it doesn't. It works fine in the LLD rule overview, but not when it has been applied to a host, in such case it shows the unreplaced $1