Keeping reference to window.opener after postback

[Todd]

I am doing some coding in a popup page which is kicked off from a parent page
(of course). When clicking on the Save button in the popup, I am attempting
to do some validation, save some data, and return a value to a control on the
parent page. To do this, I'm coding the validation and saving in the clicked
event of the button on the popup. At the end of that event, I use
RegisterStartupScript to add javascript to the page that will populate the
control on the parent page and close the popup. The problem is that the
reference to window.opener is lost as far as I can tell after the postback.
Is there a better way to do this?
--

Thanks in advance,

Todd