Well, if your hostname is only set up to resolve to a single IP address in your DNS then that's fine. If you want it to resolve to multiple addresses you will need to talk to your DNS maintainer and have them modify the zone so that it does (as happens with www.perlmonks.org).

Maybe it's a round robin setup (multiple addresses for a name, only one gets send to the client at any given time)

Lookup type ANY should give more informations, but that also depends on the server configuration.