I'm using the highlight() method to add the errorClass to the label as well as to the invalid element, like in the second example of the highlight method: http://docs.jquery.com/Plugins/Validation/validate#toptions.

So, if I submit the form with errors, the input and the label are now in red ... But if I submit it again, some labels disappear!

Here is a testcase: http://yann.universfantastiques.org/tests/jquery-validator/ where you can see the form and the js (validator options) I use.

You can see the label "Cochez cette case si vous n'avez pas de domaine chez Gandi" disappear if you hit 2 times the Enter key.
I you select "Hébergement" from the first select, you can see the same appens to the "Cochez cette case si vous n'avez pas encore de serveur" label!

I have no idea why the hideErrors() method is called! :-/