is_admin() returns true when using admin-ajax.php from front end script
WordPress sets is_admin() to true for all ajax requests (front-end or admin-side). (See codex). There’s isn’t away of over-riding this (and you shouldn’t anyway). If your ajax request can be fired from both front-end and admin side, then you may want to include whether it ‘is admin’ or not when you post the data. But … Read more