Fix in CRM-14065 for status/date mismatch warning on activities doesn't seem to work
And on the public demo it doesn't seem to work either. The problem is the use of setHours() in activityStatus in templates/CRM/Activity/Form/ActivityJS.tpl.
Where it says
var // Ignore time, only compare dates today = new Date().setHours(0,0,0,0), activityStatusId = cj('#status_id').val();
it should be
var // Ignore time, only compare dates today = new Date(), activityStatusId = cj('#status_id').val(); today.setHours(0,0,0,0);
because setHours() returns a timestamp and updates the object directly, and doesn't return a new Date object.