This may seem like a technical legal issue but it has far reaching implications for prisoners sentenced to death. Indiana killed Gregory Scott Johnson without a federal court even looking at his claims because his attorney filed his federal habeas petition one day late. If today's ruling had been in effect at the time Johnson's attorney filed his petition late, he would at least have the chance to argue that his attorney was negligent in missing the deadline. At the time, no such exception existed.
The name of the case is Holland v. Florida; the full text of the ruling is on the court's website: