kustomize: Error when composing several identical bases that use the same var: "var ... already encountered"

Here is a reduced test case and README: https://github.com/gobengo/kustomize-issue-7f53131c-0253-45a9-87c4-c6ab2f4d55ea

If you run kustomize build . in the root directory, you get an error like:

Error: accumulating resources: recursed merging from path '2cbace6b-c9f0-4f56-aba7-b911c0c85d48': var 'MYSQL_SERVICE' already encountered

The var referenced in the error message is defined in the kustomization.yaml of the (remote) base that both top-level bases use. https://github.com/gobengo/etherpad-lite/blob/master/lib/kubedb-mysql-etherpad-lite/kustomization.yaml#L6

The root directory kustomization simply composes the two directories in here (which are identical and both use etherpad-lite as a base).

kustomize build in either of the base directories works fine and produces a stream of yaml output (try ls -d */ | xargs -L1 kustomize build).

Expected Behavior: I can kustomize build . in the root directory and there is no error and I see the same output as concatenating the outputs of the two bases (joined with ‘—’).

It seems like this should work. My goal is just to have the same remote kustomization running in two different namespaces. I also want the remote kustomization to surive namePrefix so it can be used twice in the same namespace (which is why I’m using vars for the service name). Is this a bug or am I missing something about how vars should work?

EDIT:

• I tested with kustomize 2.1.0

Update 20190807: I tested with kustomize 3.1.0 and the same error happens: kubectl kustomize github.com/gobengo/kustomize-issue-7f53131c-0253-45a9-87c4-c6ab2f4d55ea.