jquery-validation: grouped Date-Select: error message disappears even if the group is considered invalid

when selects are grouped together, error message handling is wired. even when one of the fields of the group is considered invalid, no error message is rendered.

see https://jsfiddle.net/wzbptn6z/2/

I am opening this issue mostly for discussion purposes, as I am not 100% confident that it is something which need to be handled by jquery-validation core, as the behaviour seems to only occur because of the onfocusout triggered validation.