Time also matters (date fields also has time, usually it's set to 0 am). Check in your database what time is associated with the date. If the time is i.e. 11 am or even 00:00:01 am (H.m.s), it will be excluded. It also can be changed the base date by your settings. (i.e. when you create a new date it can be created by default to 0 o'clock and to 12 o'clock too. Or even it can be the node creation time too.
Please note, when you compare date/time most probably the UNIX timestamp will be compared (in views at least)! Reason: drupal save UNIX timestamps into the database, when you create a view you will see the relation is in the query, so the inputed date will be converted to timestamp and a default time. And this default time can be mess up the things.