Has anyone figured this out yet? I am having the same problem.
Only thing I can think to do is remove the sidebars code entirely from the parents functions.php found at:
function twentyten_widgets_init() {
// Area 1, located at the top of the sidebar.
register_sidebar( array(
Although this defeats the purpose of child themes and NOT needing to modify your parent theme. It seems like a simple mod post upgrade though.