Tab form onShow triggers before tabIndex updated?

In our solution we have forms on tabs that run an onShow method that sometimes needs to reference the current tab index of the tab panel. In web client, if I switch from tab 1 to tab 2 where tab 2 contains a form with an onShow method and then check in that method the tab index it returns 2 as the current tab index. In NG client it still returns 1 as the current tab index - the tab index returned by elements.tabpanel.tabIndex does not appear to update until AFTER the onShow method for the form on the new tab has already triggered.

Is this a recognised change of behaviour or a bug?