I tested the scenario you describe and I noticed two issues:
1) The OK button looks as being focused but it is actually not (if you press Enter the alert will not disappear). This is expected and the behavior is related to default button setting, you can easily reproduce it by using a standard IFRAME element.
2) After you click the OK button the focus is not returned as you describe.
What I can suggest is to add a close handler to the alert dialog and set the focus back to the button by using the focus() method.
On a side note, forums are considered community resources and we do not ensure a fast reply here - if you want to make sure that you will get an accurate and fast reply, please use our support system and open support tickets.