helm: Helm should not ignore namespace passed on command line

I have the prometheus operator running in my cluster. I want to test a new version of the prometheus operator by running it in a separate namespace. I used the “–namespace” option with the existing release name. Instead of deploying into the namespace that I specified with the “–namespace” option, it prints a warning and deploys into the original namespace.

helm upgrade --install --namespace jko-test prometheus-operator helm-charts/prometheus-operator-0.22.0
WARNING: Namespace "jko-test" doesn't match with previous. Release will be deployed to monitoring
Release "prometheus-operator" has been upgraded. Happy Helming!

While I understand the motivation to use the original namespace I think it’s the wrong thing to do here. If the user specifically asks for a namespace and it doesn’t match the original helm should exit with an error.

Output of helm version:

$ helm version
Client: &version.Version{SemVer:"v2.9.1", GitCommit:"20adb27c7c5868466912eebdf6664e7390ebe710", GitTreeState:"clean"}
Server: &version.Version{SemVer:"v2.9.1", GitCommit:"20adb27c7c5868466912eebdf6664e7390ebe710", GitTreeState:"clean"}

Output of kubectl version:

$ kubectl version
Client Version: version.Info{Major:"1", Minor:"10", GitVersion:"v1.10.2", GitCommit:"81753b10df112992bf51bbc2c2f85208aad78335", GitTreeState:"clean", BuildDate:"2018-04-27T09:22:21Z", GoVersion:"go1.9.3", Compiler:"gc", Platform:"darwin/amd64"}
Server Version: version.Info{Major:"1", Minor:"9+", GitVersion:"v1.9.4-2+4551f1c28fa6c7", GitCommit:"4551f1c28fa6c7a06ae19701bb14a3a8eacf0caf", GitTreeState:"clean", BuildDate:"2018-03-13T14:25:14Z", GoVersion:"go1.9.3", Compiler:"gc", Platform:"linux/amd64"}

Cloud Provider/Platform (AKS, GKE, Minikube etc.):