I'm not sure whether this is a bug or feature.

To reproduce:
1) go to Configuration of network maps menu;
2) click the Edit link of a map;
3) set Host label type to Custom label;
4) in the below text area enter

{HOSTNAME} {IPADDRESS};
5) save;
6) open the map in the editor, see that host label is shown as "{HOSTNAME}

{IPADDRESS}";
6) go to network maps monitoring, open the map, see that {HOSTNAME} {IPADDRESS}

are substituted with the respective values as expected.