User macro does not allowed to be used in the simple checks

I managed to reproduce this bug starting from the Zabbix frontend 1.8.4. and in the current trunk.

Try to create the simple check with the key "ssh,{$SSH_PORT}"
We receive an error "Error in item key: invalid character '{' at position 4" in the 1.8.4
and error "Error in item key: Invalid item key format." in the 1.8.8rc2

This key (DB edited directly) works well at the zabbix_server side.

On the documentation page this key even described as an example:
http://www.zabbix.com/documentation/1.8/manual/config/macros