I've created a new ticket (http://dev.jquery.com/ticket/2359) with a patch for a quirky bug I've discovered, which may or may not be a bug in the .show() method of jQuery itself, or perhaps just a bug within the validation plugin.
The problem is manifest when error messages are configured to be displayed within inline elements (which is the default case, using label elements) and a given error message container is displayed, hidden, then displayed a second time (an example scenario where this could happen in normal usage might be a user typing into a field which has both minimum and maximum length requirements). Once shown the second time, the element has somehow received block display mode, which appears to originate from the .show() method. I'm not absolutely certain though, so I'd be interested to hear likely possible causes. I have heard that this method is supposed to pick up the original DOM state display mode for the element, so it ought to act as a toggle rather than overriding it explicitly with display:block, so this may actually be a problem with the plugin.
