Description:
------------
When the year changes it displays not the expected results

Reproduce code:
---------------
<?php
for($i=0; $i<7; $i++) {
    echo date("o-m-d", mktime() + $i * 86400);
    echo '<br />';
}
?>

Expected result:
----------------
2009-12-31
2010-01-01
2010-01-02
2010-01-03
2010-01-04
2010-01-05
2010-01-06

Actual result:
--------------
2009-12-31
2009-01-01
2009-01-02
2009-01-03
2010-01-04
2010-01-05
2010-01-06