Hey All,
I've just discovered and fixed a small problem in the "Recent Posts" widget.
Basically this widget creates a second "loop" and will side effect several of the post globals (like $id and $post). The result will effect any downstream plugin that thinks it can count on these globals being available. This can also manifest in any theme (like Tarski) that has post related template calls AFTER the side bar widget.
I've fixed this problem but saving $post in a local variable and then resetting it after the loop call. I also call setup_postdata() to restore the other globals.
I just checked the latest version of widgets.php from "http://svn.wp-plugins.org/widgets/trunk/" and it still has this issue in it.
Any suggestions on how to add this to a bug list somewhere.
Sorry for being out of the loop on this process.
I'll put the diff up on my development blog.