$ cat tprs.yml
apiVersion: extensions/v1beta1
description: A foo
kind: ThirdPartyResource
metadata:
  name: foo.foo.example.com
versions:
- name: v1

---
apiVersion: extensions/v1beta1
description: A bar
kind: ThirdPartyResource
metadata:
  name: bar.bar.example.com
versions:
- name: v1
$ kubectl create -f tprs.yml 
thirdpartyresource "foo.foo.example.com" created
thirdpartyresource "bar.bar.example.com" created
$ kubectl get foos
error: unknown api group/version: foo.example.com/v1, Kind=Foo
$ kubectl get bars
error: unknown api group/version: bar.example.com/v1, Kind=Bar
$ kubectl get bars
error: unknown api group/version: bar.example.com/v1, Kind=Bar
$ kubectl get bars
$ kubectl get foos
$ kubectl get foos
error: unknown api group/version: foo.example.com/v1, Kind=Foo
$ kubectl get foos
$ kubectl get foos
$

diff --git a/pkg/apimachinery/registered/registered.go b/pkg/apimachinery/registered/registered.go
index c1e1511..110ef1b 100644
--- a/pkg/apimachinery/registered/registered.go
+++ b/pkg/apimachinery/registered/registered.go
@@ -202,7 +202,7 @@ func AddThirdPartyAPIGroupVersions(gvs ...unversioned.GroupVersion) []unversione
        for ix := range filteredGVs {
                next[ix] = filteredGVs[ix]
        }
-       thirdPartyGroupVersions = next
+       thirdPartyGroupVersions = append(thirdPartyGroupVersions, next...)

        return skippedGVs
 }