Steps to reproduce:

1. Create a passive proxy
2. Create a host using this passive proxy. Use SNMPv2, and set a macro for the community. For example {$SNMP_COMMUNITY}.
3. Create an item for that host. Example in screenshot
4. Test the item. The proxy queries the host using '{$SNMP_COMMUNITY}' in stead of the value of {$SNMP_COMMUNITY}. If the community string is as is configured (not with a macro), then it works.