Supreme Court calls takeback on earlier decsion?

Very interest in change of stances involving Miranda rights

The Supreme Court retreated from strict enforcement of the famous Miranda decision on Tuesday, ruling that a crime suspect's words could be used against him if he failed to clearly invoke his rights clearly and, instead, answered a single question after nearly three hours of interrogation.

In the past, the court has said the "burden rests on the government" to show that a crime suspect has "knowingly and intelligently waived" his rights.

But in a 5-4 decision Tuesday, the court said the suspect had the duty to invoke his rights. If he failed to do so, his later words can be used to convict him, the justices said..

In other words, you have the right to remain silent.. but if you choose not to do so.. tough.  

Okay, looking this entire article over... how did this get through the appeals court process in the first place?   He was told he could stay silent, and he didn't.. since when did the "right to do something" mean the "obligation to do something"?