Widgets with hundreds of sidebars stopped fully loading with WP 3.5

I have a site with hundreds of custom sidebars, and Widgets.php stopped finishing loading today with the upgrade to WordPress 3.5.

Technically, after about 10 or 20 minutes it finishes loading, but I cannot access (open) any of the sidebars to drag widgets into them.

Full disclosure: for the last few months I have had maybe 10 minute load time on the widgets page, and in order to load I would have to accept the a couple of timeout unresponsive script alerts, but today with WordPress 3.5, I no longer receive those alerts, and the pageload time is maybe triple (with again no actual access to the place widgets into the sidebars. The collapsed sidebars will not open.

http://wordpress.org/extend/plugins/custom-sidebars/