Now he name of the macro

{TRIGGER.KEY<1-9>}

completely illogical, as compared for example with macros

{ITEM.NAME<1-9>}

and

{ITEM.VALUE<1-9>}

.
It logically should look like this example

{ITEM.KEY<1-9>}

Recommended that you schedule change, maintaining backward compatibility, respectively.

See DESCRIPTION column and all will become clear.
http://www.zabbix.com/documentation/1.8/manual/config/macros