I'm curious as to why ad_returnredirect doesn't work. It looks to me as though it should be calling util_ReturnMetaRefresh for you.
Intriguingly, I do see this on my system from time to time, and I have Rob Mayoff's patch (http://www.arsdigita.com/bboard/q-and-a-fetch-msg?msg_id=0006Wr) that is supposed to keep this from happening.