I have a quick fix for this problem. It appears that the plugin indicates to pass the password in plain text but actually passes an encrypted password.
Make a copy of workflow "Clone, Windows with single NIC and credential".
Between steps getCloneSpec and cloneVM insert a scripted task.
The scripted task needs an IN and OUT binding to workflow attribute "spec".
In the task scripting section enter:
spec.customization.identity.identification.domainAdminPassword.value = "MyPasswordInPlainText";
That did the trick in my case.
Bernd