Steps to reproduce:

1. Create a host with couple of interfaces
2. Use API to remove one (not main) interface.

   {
   	"hostids": ["10337"],
   	"interfaces": [{
   		"ip": "194.168.3.1",
   		"dns": "",
   		"port": "10050"
   	}]
   }
   

Result

PHP Notice:  Undefined variable: hostids in /var/www/html/feature/ZBXNEXT-2156-5.1/ui/include/classes/api/services/CHostInterface.php on line 840"

Please check if issue exists in 4.0 or 5.0. Only 5.2.0alpha1 tested.