This occurs due to faulty plating; poor adhesion. The copper flows at a different rate than the inner core of zinc and pulls away. Looked at under high power you can actually see the zinc in the fissures. The exposed zinc core above the T goes hand in hand with this effect. Some examiners were actually listing these as doubled dies for a short period of time until they realized what was going on.
Edited by koinpro
05/31/2015 10:50 pm