It's apparantly due to a problem with the 2008 Super Duty Truck.

The mid-year version of that truck just recently began production at the Kentucky
Truck Plant. It's being described as a "last second quality control"
move.
The 2008 Super Duty Truck is a new design for what has been considered
the lifeblood vehicle for Ford in North America.
In March, sales of the diesel version of the 2008 Super Duty trucks were suspended and a recall issued after reports of tailpipe fires.