I have a page with SmartNav, that contains a linkbutton with a
PostBackUrl.

I have found that the page that is the target of the PostBackUrl will
have it’s postback property fired 2 times, and unfortunately, the 2nd
time it is fired the “PreviousPage” is set to Nothing.

I have posted a few places to see if someone from MS can confirm this is a bug, but  I am betting they are going to tell me to not use smartnav.