No such luck. I deleted it and uploaded it via FTP from scratch. I also used cforms' own uninstall routine and deleted ALL cforms data and started over from scratch. It seems unlikely that an intermittent bug like the ones you describe would manifest itself on four separate installations (one of which is not a 2.6->2.7 upgrade).
Very specifically, this is how I'm seeing this bug.
1 - Go to the WP Admin screen.
2 - Click on the cformsII item on the left. It should auto-expand.
3 - Hover over the "Posts" menu and click on the down arrow on the right side of the menu bar. If it's expanded, it won't shrink back down. If it's shrunken, it won't expand.
You can repeat step 3 for any of menus. None of them will expand/contract to show/hide their submenus. You can also repeat step 3 by clicking on the double-left arrow right underneath the Dashboard item. It's supposed to iconify the menu. It doesn't if I'm in any of the cformsII menus. Other plugins that add their own top-level menu item (e.g. Lester Chan's email, database, and ratings plugins) don't exhibit this behavior, so it's not a problem inherent with WordPress 2.7 itself. This is more of a problem when the menus are already iconified (no text), because then they don't work at all from any of the cforms config screens.
All other aspects of cforms seem to work fine. The AJAX features in the cforms config screens themselves work. It's only the WP admin menu AJAX features that show a problem. And this problem exists whether cforms was upgraded automatically or via FTP, whether WordPress was upgraded from 2.6 to 2.7 or a straight 2.7 install, and whether or not I tell cforms to delete all of its config data from the database.
I've confirmed that the bug exists in IE7 as well, so it's not browser-dependent.