mdnsresponder or incorrect hostname resolving

LS,

I'migrated a virtual host (in apache httpd) from one system/server to another. And in the original server a proxy pass to the new server. And I've changed the IP address in DNS. I've used 'killall mDNSResponder' to force a DNS cache flush. And at that moment a ping using the virtual hostname goes to the new (correct) server. Yet after a minute or so, a ping using the same virtual server goes to the old (incorrect) server. This is driving me crazy. It seems that bonjour is scanning the network for virtual webservers...

This happens in Mac OS High Sierra and OS X El Capitan.

How come?

Kind regards, Edgar Matzinger.