Disappearing sidebars

I have had a recurring problem of disappearing sidebars. I’m using the ModernPaper 3-column theme from performancing and the two sidebars seem to disappear without warning and seemingly without cause (though I know there is one).

Yesterday it happened approximately a half hour after a post had been made. I have cleaned up the html of the posts and have even gone in and deleted the post that immediately preceded the disappearance to no effect.

The generated source includes the following at the bottom of the page:

</blockquote></div>

<!-- begin l_sidebar -->

	<div id="l_sidebar">
	<ul id="l_sidebarwidgeted">

	</ul></div></div></body></html>

There’s no blockquote to be closed, and it never calls up the right sidebar (and only gets the top line of the left sidebar.

I’m not sure what is causing the close blockquote command, as it’s not coming from a post. The last time this happened I went through and deactivated a bunch of plugins (never reactivated them) and it seemed to resolve itself.

I’d appreciate any help out there. The page is here