You can run below command to remove the taint from master node and then you should be able to deploy your pod on that node
kubectl taint nodes mildevkub020 node-role.kubernetes.io/master-
kubectl taint nodes mildevkub040 node-role.kubernetes.io/master-
Now regarding why its showing as master node check the command you ran to join the node with kubeadm. There are separate commands for master and worker node joining.