Facebook Callback JSON does not return email sometimes

Facebook Graph API.

I am requesting email permission and it works all fine except for some users, the json does not return email field. I am not sure why this happens. The code is same and it works great for all users, returns email field except 1 in 100 or so users where it does not have this field in json. All other fields are there.

Has anyone faced this problem before ??

I checked the facebook privacy settings and there is nothing that prevents email from coming in json if user grants email access to facebook app, yet this is happening to me. I searched the net and no one else seems to be facing this issue.

Any hint would be appreciated