Dropbox invalid redirect_uri, must be an absolute uri

Digging in a bit deeper and looking at this code fragment:

this._oauth2State = Guid.NewGuid ().ToString ("N");
				var authorizeUri = DropboxOAuth2Helper.GetAuthorizeUri (OAuthResponseType.Token, DropboxAppKey, RedirectUri, this._oauth2State, false, false, null, true); //force re-authenticate
				var webView = new WebView { Source = new UrlWebViewSource { Url = authorizeUri.AbsoluteUri } };
				webView.Navigating += async (sender, e) => {
					if (!e.Url.StartsWith (RedirectUri, StringComparison.OrdinalIgnoreCase)) {
						// we need to ignore all navigation that isn't to the redirect uri.
						return;
					

the e.Url used to match the RedirectUri, and now it doesn't. Instead, the e.Url now contains the RedirectUri as a query string parameter as follows:

https://www.dropbox.com/oauth2/authorize?response_type=token&client_id=<hidden>&redirect_uri=<encoded_redirect_uri>&state=7396a67d6c604d45899fd5c588877d1f&force_reauthentication=true

Is there something more that I am missing?