Trying that, we saw also memory leaks with the plugin functions. So we checked our plugin functions and found a couple of places, where our plugin would not free references correctly. That is fixed for next version.
Please try to use WebView.Create, do something with the WebViewer like loading a website there and later call WebView.Close to remove the WebViewer. Let us know if you still find a way, where we leak memory or any problem you may find with next plugin.
PS: Our MBS Xojo Win Plugin also gets a few similar fixes.