This bug in all version of cs2008 (cs2008,cs2008sp1,cs2008.5b1) .
If your setup your timezone not GMT (eq.GMT-8) , you will find Publication date will decrease or increase in blog post.
For example:
If original Publication date is 2008/09/02 11:00PM , when you enter edit post , the publication date is show 2008/09/02 03:00PM (in GMT-8), when you save it and publication date will decrease 8 hours of original post.
This bug only find in edit Blog post , because only blog allow you change publication date.