I've just updated to 2009 Vol 1, and as the subject says the SelectedRows are cleared on any PostBack.
Firstly, I thought it may be an issue with WARPS, so I removed them all.
Secondly, I thought it may be an issue with IE8, but the problem still exists in IE7 compatibility mode and FF3.
Please note, I am not rebinding the data on PostBack.
I reported a similar issue in Feb 2008 in version 20081.1000 which was fixed by hotfix 2013.