drupal_validate_form() cannot be used twice on the same form

drupal_validate_form() caches $validated_forms. This means that you cannot call the same form twice via drupal_execute() in one page view safely. The second and all successive calls will not call the form's validate function. Instead, they will pass on to the submit.

My proposed fix to this bug will address all uses of static caching arrays like this one throughout core and contrib; they all have to go, but without killing the corresponding performance benefit. I'll be proposing a solution on the dev mailing list soon.