Sending contacts in WhatsApp shows "Unnamed" contacts

Whenever I try to send contact in WhatsApp, by clicking on the "Attachment" icon during a chat, my contact list shows me a lot of "Unnamed" contacts. After scrolling past them I am able to see my contacts.

Where do these "Unnamed" contacts come from? I cannot see them when I open up my People app. Is it a problem with WhatsApp or my device?

I have HTC One X running Android 4.2.2 with Sense 5.