Wrong date format in profile plugin
From Joomla! Documentation
If you see % (ampersand) in your date field, which is part of the profile plugin (date of birth field), you can fix it easily with editing the file plugins/user/profile/profile.php.
Line #227 currently (Joomla! 2.5.1) is:
$data['profile']['dob'] = $date->format('%Y-%m-%d');
and should be changed to:
$data['profile']['dob'] = $date->format('Y-m-d');
- issue in the tracker (bug tracker #27918)