diff --git a/moto/backends.py b/moto/backends.py
index 5d48b124b..5847ad85e 100644
--- a/moto/backends.py
+++ b/moto/backends.py
@@ -2,6 +2,7 @@ from __future__ import unicode_literals
 
 import importlib
 import moto
+import sys
 
 
 decorators = [
@@ -26,8 +27,16 @@ def backends():
         yield _import_backend(module_name, backends_name)
 
 
-def named_backends():
-    for name, (module_name, backends_name) in BACKENDS.items():
+def loaded_backends():
+    loaded_modules = sys.modules.keys()
+    loaded_modules = [m for m in loaded_modules if m.startswith("moto.")]
+    imported_backends = [
+        name
+        for name, (module_name, _) in BACKENDS.items()
+        if f"moto.{module_name}" in loaded_modules
+    ]
+    for name in imported_backends:
+        module_name, backends_name = BACKENDS[name]
         yield name, _import_backend(module_name, backends_name)
 
 
diff --git a/moto/core/models.py b/moto/core/models.py
index 885a2ad45..3857908f7 100644
--- a/moto/core/models.py
+++ b/moto/core/models.py
@@ -840,7 +840,7 @@ class MotoAPIBackend(BaseBackend):
     def reset(self):
         import moto.backends as backends
 
-        for name, backends_ in backends.named_backends():
+        for name, backends_ in backends.loaded_backends():
             if name == "moto_api":
                 continue
             for region_name, backend in backends_.items():
diff --git a/moto/mediapackage/models.py b/moto/mediapackage/models.py
index 1e6fb9940..744a3fd21 100644
--- a/moto/mediapackage/models.py
+++ b/moto/mediapackage/models.py
@@ -74,13 +74,13 @@ class MediaPackageBackend(BaseBackend):
     def __init__(self, region_name=None):
         super(MediaPackageBackend, self).__init__()
         self.region_name = region_name
+        self._channels = OrderedDict()
+        self._origin_endpoints = OrderedDict()
 
     def reset(self):
         region_name = self.region_name
         self.__dict__ = {}
         self.__init__(region_name)
-        self._channels = OrderedDict()
-        self._origin_endpoints = OrderedDict()
 
     def create_channel(self, description, id, tags):
         arn = "arn:aws:mediapackage:channel:{}".format(id)
diff --git a/moto/server.py b/moto/server.py
index 18d741642..88ae89768 100644
--- a/moto/server.py
+++ b/moto/server.py
@@ -68,10 +68,13 @@ class DomainDispatcherApplication(object):
             if pattern.match("http://%s" % host):
                 return backend
 
-        print(
-            "Unable to find appropriate URL for {}."
-            "Remember to add the URL to urls.py, and run script/update_backend_index.py to index it."
-        )
+        if "amazonaws.com" in host:
+            print(
+                "Unable to find appropriate backend for {}."
+                "Remember to add the URL to urls.py, and run script/update_backend_index.py to index it.".format(
+                    host
+                )
+            )
 
     def infer_service_region_host(self, environ):
         auth = environ.get("HTTP_AUTHORIZATION")