Ok, by comparing the User skin object and the account login module I've come up with a fix. Not sure how to post bugs to Gemin ior whatever it is, but if anyone wants to fix theirs open up Admin\Authentication\Login.ascx.vb and alter the cmdRegister event. I left the original code in there commented out for comparison.

        Private Sub cmdRegister_Click(ByVal sender As Object, ByVal e As EventArgs) Handles cmdRegister.Click

            'If PortalSettings.UserRegistration <> PortalRegistrationType.NoRegistration Then
            '    If PortalSettings.UserTabId <> -1 Then
            '        ' user defined tab
            '        Response.Redirect(NavigateURL(PortalSettings.UserTabId, "", "returnurl=" & HttpUtility.UrlEncode(HttpContext.Current.Request.QueryString("returnurl"))), True)
            '    Else
            '        ' portal tab
            '        If PortalSettings.HomeTabId <> -1 Then
            '            Response.Redirect(NavigateURL(PortalSettings.HomeTabId, "Register", "returnurl=" & HttpUtility.UrlEncode(HttpContext.Current.Request.QueryString("returnurl"))), True)
            '        Else
            '            Response.Redirect(NavigateURL("Register", "returnurl=" & HttpUtility.UrlEncode(HttpContext.Current.Request.QueryString("returnurl"))), True)
            '        End If
            '    End If
            'End If
           
        If PortalSettings.UserRegistration <> PortalRegistrationType.NoRegistration Then
             Dim ReturnUrl As String = HttpContext.Current.Request.RawUrl
        If ReturnUrl.IndexOf("?returnurl=") <> -1 Then
            ReturnUrl = ReturnUrl.Substring(0, ReturnUrl.IndexOf("?returnurl="))
        End If
        ReturnUrl = HttpUtility.UrlEncode(ReturnUrl)

        If PortalSettings.UserTabId <> -1 Then
            ' user defined tab
            Response.Redirect(NavigateURL(PortalSettings.UserTabId, "", "returnurl=" & ReturnUrl), True)
        Else
            ' portal tab
            If PortalSettings.HomeTabId <> -1 Then
                Response.Redirect(NavigateURL(PortalSettings.HomeTabId, "Register", "returnurl=" & ReturnUrl), True)
            Else
                Response.Redirect(NavigateURL("Register", "returnurl=" & ReturnUrl), True)
            End If
        End If
         End If

        End Sub

Thanks for posting this.  I was very surprised that the registration feature had been broken and had sweat dripping from my glasses until I found it. 

Best wishes on you for the good work!