Use defined host when not equal to target

internal/manifest/manifest.go

@@ -75,13 +75,18 @@ func (m Manifest) Update(images []string) Manifest {
 		//
 		// In the event the source cannot be found in the manifest, we must rely on
 		// trying to find the source registry from the repository the image is sourced from.
-		//
-		// This is more of a nice-to-have. The worst case is that we get it wrong and the
-		// user has to update the host value to the correct one. Once defined in the manifest
-		// we can continue to use the host that was set.
 		foundSource, exists := m.findSourceInManifest(updatedImage)
 		if !exists {
-			updatedSource.Host = getSourceHostFromRepository(updatedRegistryPath.Repository())
+
+			// When the source host and the target host are the same, this means that the
+			// images that were retrieved are target images.
+			//
+			// When the source host and target host are different, we can safely use the
+			// host found in the image definition as the source.
+			updatedSource.Host = updatedRegistryPath.Host()
+			if updatedRegistryPath.Host() == m.Target.Host {
+				updatedSource.Host = getSourceHostFromRepository(updatedRegistryPath.Repository())
+			}
 
 			updatedRepository := updatedRegistryPath.Repository()
 			updatedRepository = strings.Replace(updatedRepository, m.Target.Repository, "", 1)