Cannot edit existing posts after upgrading to 2.0

Having a weird effect with one blog post-upgrade. Everything seems to work correctly, including writing a new post, EXCEPT for editing existing posts. That does not work; what happens when I click Edit from the Manage page is that the Write page opens, the CSS is loaded (I can see the editor switch to the toolbar-enabled view, is what I mean) and then the page jumps to the permalink for the post.

I’ve tried disabling all plugins one at a time but no change. This doesn’t happen with the other install of WP2 I have on the same server, with most of the same plugins.

Would really appreciate any constructive suggestions.